Project-aware assist, link suggestions, project-scoped RAG, semantic search tool, SSE race fix

- Writing assistant: inject project notes as context (definition-tagged first), wikilink suggestions
- Link suggestions: server-side endpoint finds unlinked term occurrences, NoteEditorView sidebar panel
- Project-scoped RAG: ChatView ProjectSelector filters semantic+keyword search to selected project
- Semantic search tool: LLM search_notes upgraded to hybrid semantic (0.40 threshold) + keyword merge
- SSE race condition fix: drain remaining events after stream loop exits in chat.py and notes.py
- RAG_AUTO_SNIPPET raised 800→4000; sidebar include uses full note body; MAX_BODY_CHARS 8000→24000
- Enter-to-submit on writing assistant instruction textareas (note and task editors)
- DiffView: equal-line collapsing with 3-line context around changes

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

alembic/versions/0023_add_tags_to_note_versions.py

@@ -0,0 +1,16 @@
+"""Add tags column to note_versions for complete version snapshots."""
+
+from alembic import op
+
+revision = "0023"
+down_revision = "0022"
+
+
+def upgrade() -> None:
+    op.execute(
+        "ALTER TABLE note_versions ADD COLUMN IF NOT EXISTS tags TEXT[] NOT NULL DEFAULT '{}'"
+    )
+
+
+def downgrade() -> None:
+    op.execute("ALTER TABLE note_versions DROP COLUMN IF EXISTS tags")