docs: comprehensive documentation refresh — remove stale references, add missing content

Root documentation:
- README.md: add Datums description, update addon load order and SDK references,
  fix project structure tree, update issue reporting guidance
- CONTRIBUTING.md: update submodule table (remove ztools, add gears/datums/solver),
  fix QSS guidance (single canonical source, not three copies)
- docs/ARCHITECTURE.md: update bootstrap flow (5 addons, split deferred timers
  between Create core and Silo addon), update load order and source layout
- docs/COMPONENTS.md: add Datums and Solver sections, update Gears description,
  fix Silo origin registration reference
- docs/KNOWN_ISSUES.md: create missing file referenced by CLAUDE.md and CONTRIBUTING.md
- docs/INTEGRATION_PLAN.md: update layer 5 diagram, fix load order references,
  update Phase 6 install rules, fix Layer 2/3/5 descriptions
- docs/OVERVIEW.md: add datums submodule entry
- docs/UPSTREAM.md: update Phase 1 directory table and Phase 4 submodule list

mdBook documentation (docs/src/):
- SUMMARY.md: replace dead architecture/ links with existing reference pages,
  remove deleted silo-server files, add new silo-server pages
- introduction.md: rewrite — replace ztools with current addons (Silo, Gears,
  Datums, KCSDK), update version to v0.1.5/FreeCAD 1.2.0
- guide/getting-started.md: update first-run addon list
- guide/installation.md: update verification console output
- guide/workbenches.md: rewrite — replace ztools with Gears, Datums, Solver
- guide/building.md: update submodule table, fix error message guidance
- development/contributing.md: fix scope example and issue reporting
- development/repo-structure.md: rewrite — add SDK, datums, gears, solver,
  reference/ folder; update submodule and key files tables
- development/writing-an-addon.md: fix priority range table
- reference/create-module-bootstrap.md: rewrite — reflect addon_loader system,
  split deferred timers between Create core and Silo addon
- reference/datum-creator.md: update from ZTools to datums addon paths and naming
- reference/glossary.md: add KCSDK entry, update FreeCAD version, remove ztools
  entry, update repository URLs table

docs/INTEGRATION_PLAN.md

@@ -1,10 +1,10 @@
 # Integration Plan
 
-Strategy for integrating ztools and Silo as built-in addons while maintaining clear boundaries with FreeCAD core.
+Strategy for integrating Kindred addons as built-in components while maintaining clear boundaries with FreeCAD core.
 
 ## Goals
 
-1. **Native feel** -- ztools and Silo behave as first-class citizens, not bolted-on addons
+1. **Native feel** -- Addons behave as first-class citizens, not bolted-on extras
 2. **Clean boundaries** -- Clear separation between FreeCAD core, Kindred extensions, and addon code
 3. **Minimal core modifications** -- Preserve FreeCAD's container models (Part, Body, Assembly)
 4. **Maintainability** -- Easy to pull upstream FreeCAD changes without merge conflicts
@@ -18,12 +18,11 @@ Strategy for integrating ztools and Silo as built-in addons while maintaining cl
 ├─────────────────────────────────────────────────────────────┤
 │  Layer 5: Kindred Addons (mods/)                            │
 │  ┌──────────────────┐  ┌──────────────────┐                 │
-│  │      Silo        │  │      Gears       │                 │
-│  │  Open/Save/Commit│  │  Parametric gear │                 │
-│  │  Part numbering  │  │  generation      │                 │
-│  │  Revision control│  │                  │                 │
-│  │  BOM management  │  │                  │                 │
-│  └──────────────────┘  └──────────────────┘                 │
+│  ┌──────────┐ ┌──────────┐ ┌──────────┐ ┌──────────┐       │
+│  │   Silo   │ │  Gears   │ │  Datums  │ │  Solver  │       │
+│  │ PLM/VCS  │ │ Gear gen │ │ Datum    │ │ Assembly │       │
+│  │ BOM mgmt │ │          │ │ creator  │ │ research │       │
+│  └──────────┘ └──────────┘ └──────────┘ └──────────┘       │
 ├─────────────────────────────────────────────────────────────┤
 │  Layer 4: Kindred Addon SDK (mods/sdk/)                     │
 │  ┌─────────────────────────────────────────────────────────┐│
@@ -58,7 +57,7 @@ FreeCAD's fundamental data structures: `PartDesign::Body`, `PartDesign::Pocket`,
 
 ### Layer 2: FreeCAD Python API -- use as-is
 
-The Python API provides everything needed for feature creation, command registration, and geometry access. ZTools and Silo operate entirely through this layer. Stable FreeCAD APIs (`Gui.addCommand()`, `Gui.addWorkbench()`, `Gui.addWorkbenchManipulator()`) are called directly — they do not need SDK wrappers.
+The Python API provides everything needed for feature creation, command registration, and geometry access. Addons operate through this layer. Stable FreeCAD APIs (`Gui.addCommand()`, `Gui.addWorkbench()`, `Gui.addWorkbenchManipulator()`) are called directly -- they do not need SDK wrappers.
 
 ### Layer 3: Kindred Create Module -- `src/Mod/Create/`
 
@@ -67,9 +66,9 @@ The Create module serves two roles:
 **Python bootstrap** (`Init.py`, `InitGui.py`, `addon_loader.py`):
 - Scans `mods/` for `package.xml` manifests with `<kindred>` extensions
 - Validates version compatibility, resolves dependencies via topological sort
-- Loads addons in priority order (sdk → ztools → silo)
+- Loads addons in priority order (sdk → solver → gears → datums → silo)
 - Populates `FreeCAD.KindredAddons` registry for runtime introspection
-- Sets up deferred Silo dock panels, origin registration, and update checker
+- Sets up deferred .kc format registration and update checker
 
 **C++ module scaffold** (`App/`, `Gui/`, `CreateGlobal.h`):
 - `CreateApp.so` and `CreateGui.so` shared libraries
@@ -91,7 +90,7 @@ The SDK is loaded first (priority 0) and has no dependencies.
 
 ### Layer 5: Kindred Addons -- `mods/`
 
-Pure Python addons with `package.xml` manifests. Self-contained with `Init.py`, `InitGui.py`, and `<kindred>` metadata. Developed and versioned independently as git submodules. Must declare `<dependency>sdk</dependency>` to use SDK APIs. Current addons: **silo** (PLM), **gears** (parametric gear generation).
+Pure Python addons with `package.xml` manifests. Self-contained with `Init.py`, `InitGui.py`, and `<kindred>` metadata. Developed and versioned independently as git submodules. Must declare `<dependency>sdk</dependency>` to use SDK APIs. Current addons: **solver** (assembly research), **gears** (parametric gear generation), **datums** (unified datum creator), **silo** (PLM).
 
 ---
 
@@ -158,9 +157,9 @@ Theme colors are now centralized in the SDK's YAML palette (`mods/sdk/kindred_sd
 
 ### Phase 6: Build system integration -- DONE
 
-**Goal:** CMake install rules for `mods/` submodules so packages include ztools, Silo, and SDK automatically.
+**Goal:** CMake install rules for `mods/` submodules so packages include all addons automatically.
 
-**Implementation:** `src/Mod/Create/CMakeLists.txt` includes install rules for all addons (`mods/ztools`, `mods/silo`, `mods/sdk`) and the C++ module scaffold (`App/`, `Gui/`). Build-time code generation: `version.py.in` → `version.py` via `configure_file()`.
+**Implementation:** `src/Mod/Create/CMakeLists.txt` includes install rules for all addons (`mods/sdk`, `mods/solver`, `mods/gears`, `mods/datums`, `mods/silo`) and the C++ module scaffold (`App/`, `Gui/`). Build-time code generation: `version.py.in` → `version.py` via `configure_file()`.
 
 **CI/CD status:** Release workflows (`.gitea/workflows/release.yml`) build for Linux (AppImage + .deb), macOS (DMG for Intel + Apple Silicon), and Windows (.exe NSIS installer + .7z archive). Builds run on public runners in dockerized mode. Releases are triggered by `v*` tags. See `docs/CI_CD.md` for details.