Restructure chat service, web routes, and add test suite

Split monolithic chat service into modular structure with Matrix client
support, extract web server into per-resource route modules, introduce
bootstrap/main-loop separation, and add comprehensive vitest coverage
across services, repositories, and utilities. Adds project docs and
CLAUDE.md agent instructions.

src/database/client.ts

@@ -57,12 +57,23 @@ export function runMigrations(db: Database.Database): void {
       created_at INTEGER NOT NULL
     );
 
+    CREATE TABLE IF NOT EXISTS activity_log (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      timestamp INTEGER NOT NULL,
+      type TEXT NOT NULL,
+      message TEXT NOT NULL,
+      recipient TEXT,
+      image_url TEXT
+    );
+
     CREATE INDEX IF NOT EXISTS idx_posts_subreddit
       ON processed_posts(subreddit);
     CREATE INDEX IF NOT EXISTS idx_posts_processed_at
       ON processed_posts(processed_at);
     CREATE INDEX IF NOT EXISTS idx_posts_message_sent
       ON processed_posts(message_sent);
+    CREATE INDEX IF NOT EXISTS idx_activity_log_timestamp
+      ON activity_log(timestamp);
   `);
 
   // Add new columns to existing tables (safe to run multiple times)