feat: add note collaboration schema, access control, and API routes

Add noteCollaborators and noteUserState tables for sharing notes between
users. Implement access control helpers (canAccessNote, requireNoteAccess,
requireNoteOwnership) and collaborators CRUD service. Create API endpoints
for managing collaborators and searching users.

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

src/lib/server/db/index.ts

@@ -93,6 +93,21 @@ sqlite.exec(`
 		client_id TEXT NOT NULL
 	);
 
+	CREATE TABLE IF NOT EXISTS note_collaborators (
+		note_id TEXT NOT NULL REFERENCES notes(id) ON DELETE CASCADE,
+		user_id INTEGER NOT NULL REFERENCES users(id),
+		added_by INTEGER NOT NULL REFERENCES users(id),
+		added_at INTEGER NOT NULL
+	);
+
+	CREATE TABLE IF NOT EXISTS note_user_state (
+		note_id TEXT NOT NULL REFERENCES notes(id) ON DELETE CASCADE,
+		user_id INTEGER NOT NULL REFERENCES users(id),
+		pinned INTEGER NOT NULL DEFAULT 0,
+		archived INTEGER NOT NULL DEFAULT 0,
+		sort_order INTEGER NOT NULL DEFAULT 0
+	);
+
 	CREATE TABLE IF NOT EXISTS login_attempts (
 		id INTEGER PRIMARY KEY AUTOINCREMENT,
 		ip TEXT NOT NULL,
@@ -168,6 +183,10 @@ sqlite.exec(`
 	CREATE INDEX IF NOT EXISTS sync_log_timestamp_idx ON sync_log(timestamp);
 	CREATE INDEX IF NOT EXISTS login_attempts_ip_timestamp_idx ON login_attempts(ip, timestamp);
 
+	CREATE UNIQUE INDEX IF NOT EXISTS note_collaborators_unique ON note_collaborators(note_id, user_id);
+	CREATE INDEX IF NOT EXISTS note_collaborators_user_id_idx ON note_collaborators(user_id);
+	CREATE UNIQUE INDEX IF NOT EXISTS note_user_state_unique ON note_user_state(note_id, user_id);
+
 	CREATE TABLE IF NOT EXISTS api_keys (
 		id TEXT PRIMARY KEY,
 		user_id INTEGER NOT NULL REFERENCES users(id),