fix: Fallback to cached session ID in session_note_add

When session_id is not provided, falls back to getSessionId() which
reads from CLAUDE_SESSION_ID env or ~/.cache/session-memory/current_session.
Fixes NOT NULL constraint violation on session_notes.session_id.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/tools/crud.ts

@@ -14,7 +14,7 @@ import * as os from 'os';
 /**
  * Get current session ID from environment or cache file
  */
-function getSessionId(): string {
+export function getSessionId(): string {
   // Check environment first
   if (process.env.CLAUDE_SESSION_ID) {
     return process.env.CLAUDE_SESSION_ID;

src/tools/session-docs.ts

@@ -3,6 +3,7 @@
 
 import { query, queryOne, execute } from '../db.js';
 import { getEmbedding, formatEmbedding } from '../embeddings.js';
+import { getSessionId } from './crud.js';
 
 // ============================================================================
 // SESSION NOTES
@@ -32,7 +33,8 @@ interface SessionNote {
  * Auto-generates embedding for semantic search
  */
 export async function sessionNoteAdd(args: SessionNoteAddArgs): Promise<string> {
-  const { session_id, note_type, content } = args;
+  const { session_id: providedSessionId, note_type, content } = args;
+  const session_id = providedSessionId || getSessionId();
 
   // Generate embedding for semantic search
   const embedding = await getEmbedding(content);