feat(nextcloud): add Nextcloud-compatible API layer

Implement a complete Nextcloud client compatibility layer so that
Nextcloud desktop/mobile sync clients can connect to OxiCloud.

Key additions:
- Login Flow v2 (device auth) with OIDC bridge support
- WebDAV handler compatible with Nextcloud clients (PROPFIND, GET,
  PUT, DELETE, MKCOL, MOVE, COPY, HEAD, PROPPATCH)
- OCS API endpoints (user info, capabilities, notifications stubs,
  sharees, unified search)
- Basic Auth middleware with app password verification, account
  lockout integration, and blake3-keyed auth cache
- App password management: create, list, revoke via both native
  API (JWT-authenticated profile page) and Nextcloud OCS endpoints
- Nextcloud file ID mapping (oc:fileid) with persistent DB storage
- Chunked upload support (Nextcloud v2 chunking protocol)
- Trashbin WebDAV interface
- Avatar (SVG placeholder) and preview (redirect) handlers
- User profile page with app password management UI
- URL user validation on all DAV routes (403 on mismatch)
- Database schema for app_passwords and nextcloud_object_ids tables

All services are behind a `nextcloud.enabled` config flag and
cleanly separated under src/interfaces/nextcloud/.

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

.gitignore

@@ -55,6 +55,7 @@ npm-debug.log
 # Log files
 *.log
 logs/
+logs.txt
 
 # Storage data (user files, blobs — never commit)
 storage/
@@ -73,3 +74,17 @@ storage/
 *.swp
 *.swo
 nohup.out
+
+# Agent planning docs (live on 'planning' branch)
+docs/plans/
+.planning/
+
+# Local dev compose (not in upstream)
+docker-compose.dev.yml
+
+# Test scripts with hardcoded credentials
+test-nextcloud-*.sh
+
+# Claude Code artifacts
+.claude/
+CLAUDE.md