feat: add QuickNav addon — Phase 1 core infrastructure (#320)

Add quicknav submodule and create-side integration for keyboard-driven
command navigation.

Submodule: mods/quicknav (https://git.kindred-systems.com/kindred/quicknav)

Create-side changes:
- CMakeLists.txt: add quicknav install rules
- test_kindred_pure.py: add 16 workbench_map validation tests
- docs/src/quicknav/SPEC.md: QuickNav specification

QuickNav provides numbered-key access to workbenches (Ctrl+1-5),
command groupings (Shift+1-9), and individual commands (1-9), with
a navigation bar toolbar and input-widget safety guards.

.gitmodules

@@ -22,3 +22,6 @@
 	path = mods/solver
 	url = https://git.kindred-systems.com/kindred/solver.git
 	branch = main
+[submodule "mods/quicknav"]
+	path = mods/quicknav
+	url = https://git.kindred-systems.com/kindred/quicknav.git