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>

src/fabledassistant/services/embeddings.py

@@ -79,6 +79,7 @@ async def semantic_search_notes(
     exclude_ids: set[int] | None = None,
     limit: int = 8,
     threshold: float = _SIMILARITY_THRESHOLD,
+    project_id: int | None = None,
 ) -> list[tuple[float, Note]]:
     """Return up to *limit* (score, note) pairs most relevant to *query*.
 
@@ -99,6 +100,8 @@ async def semantic_search_notes(
                 .join(Note, NoteEmbedding.note_id == Note.id)
                 .where(NoteEmbedding.user_id == user_id)
             )
+            if project_id is not None:
+                stmt = stmt.where(Note.project_id == project_id)
             if exclude_ids:
                 stmt = stmt.where(NoteEmbedding.note_id.notin_(exclude_ids))
             rows = list((await session.execute(stmt)).all())