Add project CRUD API (GET/POST/PATCH/DELETE) with ownership checks and
transactional delete. Add diagram list filtering by projectId and
unorganized query params with typed Zod query schema for Hono RPC
type safety. Create DiagramSidebar with Projects tree (expand/collapse,
inline rename) and Recent tab. Add project picker to CreateDiagramDialog.
Includes 15 schema validation tests (107 total passing).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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