docs(08-04/05/06): add plan summaries — wave 2 backend decomposition complete

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/phases/08-stack-upgrade-backend-decomposition/08-05-SUMMARY.md

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+# Plan 08-05 Summary — Documents API Decomposition
+
+**Status:** Complete  
+**Requirements:** CODE-02, CODE-08  
+**Date:** 2026-06-12
+
+## What Was Done
+
+- Created `backend/api/documents/` package: `shared.py`, `upload.py`, `crud.py`, `content.py`, `__init__.py`
+- `__init__.py` aggregates with `prefix="/api/documents"` — 9 routes total
+- `_CLOUD_PROVIDERS`, `UploadUrlRequest`, `DocumentPatch` defined once in `shared.py` (CODE-08)
+- `list_documents` registered directly on parent router (FastAPI 0.128 empty-path/prefix restriction)
+- `get_storage_backend_for_document` re-exported in `__init__.py` for test monkeypatching compatibility
+- Deleted `backend/api/documents.py` monolith after 43-test regression passed
+
+## Test Results
+
+- `tests/test_documents.py`: 39 passed, 4 xfailed
+- `tests/test_shares.py`: 4 passed
+- Full suite: 405 passed