docs(sdk): document per-document origin Python bindings (#406)

- Add Per-Document Origin API section to kcsdk-python.md covering
  document_origin, set_document_origin, clear_document_origin, and
  find_owning_origin with parameter tables and usage example
- Add 4 per-document functions to kindred_sdk wrappers table showing
  the doc.Name extraction pattern
- Add Python Exposure subsection to cpp-origin-manager.md cross-
  referencing both kcsdk and kindred_sdk layers

docs/src/reference/kcsdk-python.md

@@ -180,6 +180,64 @@ Return IDs of all registered panel providers as `list[str]`.
 
 Return names of all registered providers (across all provider types) as `list[str]`.
 
+## Per-Document Origin API
+
+These functions manage explicit associations between open documents and origins. They are used by the file commands (Save, Commit, Push) to determine which origin backend handles a given document.
+
+### document_origin(doc_name)
+
+Get the origin associated with a document. Checks explicit association first, then falls back to ownership detection (`ownsDocument`).
+
+| Parameter | Type | Description |
+|-----------|------|-------------|
+| `doc_name` | `str` | FreeCAD document name (internal `Name` property) |
+
+Returns an origin info dict (`id`, `label`, `capabilities`, …) or `None`.
+
+### set_document_origin(doc_name, origin_id)
+
+Explicitly associate a document with an origin. Used when creating new documents to mark them with the origin that created them.
+
+| Parameter | Type | Description |
+|-----------|------|-------------|
+| `doc_name` | `str` | FreeCAD document name |
+| `origin_id` | `str` | Registered origin ID (e.g. `"silo"`, `"local"`) |
+
+Returns `True` on success, `False` if the document or origin ID is not found.
+
+### clear_document_origin(doc_name)
+
+Remove the explicit origin association for a document. After clearing, origin queries fall back to ownership detection.
+
+| Parameter | Type | Description |
+|-----------|------|-------------|
+| `doc_name` | `str` | FreeCAD document name |
+
+### find_owning_origin(doc_name)
+
+Scan all registered origins via their `ownsDocument` method. Unlike `document_origin`, this bypasses the explicit association cache and always re-queries.
+
+| Parameter | Type | Description |
+|-----------|------|-------------|
+| `doc_name` | `str` | FreeCAD document name |
+
+Returns an origin info dict or `None`.
+
+```python
+import kcsdk
+
+# Look up which origin handles the active document
+info = kcsdk.document_origin("MyPart")
+if info:
+    print(f"Document handled by: {info['id']}")
+
+# Force-associate a document with the Silo origin
+kcsdk.set_document_origin("MyPart", "silo")
+
+# Re-detect without cache
+owner = kcsdk.find_owning_origin("MyPart")
+```
+
 ## `kindred_sdk` Convenience Wrappers
 
 The `kindred_sdk` Python package wraps the `kcsdk` C++ module with input validation, error handling, and fallback to legacy APIs.
@@ -224,6 +282,10 @@ These mirror the `kcsdk` functions with added type validation and try/except err
 | `kindred_sdk.refresh_context()` | `kcsdk.refresh()` |
 | `kindred_sdk.register_origin()` | `FreeCADGui.addOrigin()` |
 | `kindred_sdk.unregister_origin()` | `FreeCADGui.removeOrigin()` |
+| `kindred_sdk.document_origin(doc)` | `kcsdk.document_origin(doc.Name)` |
+| `kindred_sdk.set_document_origin(doc, id)` | `kcsdk.set_document_origin(doc.Name, id)` |
+| `kindred_sdk.clear_document_origin(doc)` | `kcsdk.clear_document_origin(doc.Name)` |
+| `kindred_sdk.find_owning_origin(doc)` | `kcsdk.find_owning_origin(doc.Name)` |
 | `kindred_sdk.get_theme_tokens()` | YAML palette lookup |
 | `kindred_sdk.load_palette()` | `Palette` object from YAML |
 | `kindred_sdk.create_version()` | Kindred Create version string |