feat: implement Phase 2 (Pulse, Admin, RC2)

compose/init/05_update_posts.sql

@@ -0,0 +1,5 @@
+-- Add new columns for Blog/Pulse feature
+ALTER TABLE posts 
+ADD COLUMN IF NOT EXISTS tags JSON DEFAULT NULL,
+ADD COLUMN IF NOT EXISTS excerpt TEXT DEFAULT NULL,
+ADD COLUMN IF NOT EXISTS author VARCHAR(100) DEFAULT 'System';