docs: refactor semantic search from notes-specific to multi-app architecture

Update ADRs to reflect that vector database and semantic search support
multiple Nextcloud apps (notes, calendar, deck, files, contacts) rather
than being notes-specific. Introduce semantic:read/write OAuth scopes
to replace app-specific scope requirements for cross-app search.

Changes:
- ADR-007: Add plugin architecture (DocumentScanner, DocumentProcessor,
  DocumentVerifier) for multi-app vector sync
- ADR-008: Rename tools from nc_notes_semantic_* to nc_semantic_*, update
  scope from notes:read to semantic:read
- ADR-009: NEW - Document decision to use generic semantic:read scope
  with dual-phase authorization instead of requiring all app scopes
- oauth-architecture.md: Add semantic:read/write scope documentation
- README.md: Move semantic search to dedicated section separate from Notes

This is a breaking change that correctly positions semantic search as a
cross-app capability before broader adoption. Existing deployments will
need to re-authenticate with the new semantic:read scope.

Relates to user request to decouple vector database from notes-only model
and establish proper OAuth scope boundaries for multi-app semantic search.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

README.md

@@ -19,7 +19,8 @@ The Nextcloud MCP (Model Context Protocol) server allows Large Language Models l
 | **Deployment** | Standalone (Docker, VM, K8s) | Inside Nextcloud (ExApp via AppAPI) |
 | **Primary Users** | Claude Code, IDEs, external developers | Nextcloud end users via Assistant app |
 | **Authentication** | OAuth2/OIDC or Basic Auth | Session-based (integrated) |
-| **Notes Support** | ✅ Full CRUD + search + semantic search (9 tools) | ❌ Not implemented |
+| **Notes Support** | ✅ Full CRUD + keyword search (7 tools) | ❌ Not implemented |
+| **Semantic Search** | ✅ Multi-app vector search (2+ tools) | ❌ Not implemented |
 | **Calendar** | ✅ Full CalDAV + tasks (20+ tools) | ✅ Events, free/busy, tasks (4 tools) |
 | **Contacts** | ✅ Full CardDAV (8 tools) | ✅ Find person, current user (2 tools) |
 | **Files (WebDAV)** | ✅ Full filesystem access (12 tools) | ✅ Read, folder tree, sharing (3 tools) |
@@ -200,7 +201,7 @@ For a complete list of all supported OAuth scopes and their descriptions, see [O
 
 | App | Tools | Read Scope | Write Scope | Operations |
 |-----|-------|-----------|-------------|------------|
-| **Notes** | 9 | `notes:read` | `notes:write` | Create, read, update, delete, search notes (keyword + semantic) |
+| **Notes** | 7 | `notes:read` | `notes:write` | Create, read, update, delete, search notes (keyword search) |
 | **Calendar** | 20+ | `calendar:read` `todo:read`  | `calendar:write` `todo:write`   | Events, todos (tasks), calendars, recurring events, attendees |
 | **Contacts** | 8 | `contacts:read` | `contacts:write` | Create, read, update, delete contacts and address books |
 | **Files (WebDAV)** | 12 | `files:read` | `files:write` | List, read, upload, delete, move files; **OCR/document processing** |
@@ -208,6 +209,7 @@ For a complete list of all supported OAuth scopes and their descriptions, see [O
 | **Cookbook** | 13 | `cookbook:read` | `cookbook:write` | Recipes, import from URLs, search, categories |
 | **Tables** | 5 | `tables:read` | `tables:write` | Row operations on Nextcloud Tables |
 | **Sharing** | 10+ | `sharing:read` | `sharing:write` | Create, manage, delete shares |
+| **Semantic Search** | 2+ | `semantic:read` | `semantic:write` | Vector-powered semantic search across **all apps** (notes, calendar, deck, files, contacts), background indexing |
 
 #### Document Processing (Optional)