refactor: migrate to sqlite

hub/internal/migrations/20260415151037_create_agent_table.up.sql

@@ -1,14 +1,14 @@
 CREATE TABLE agents (
-    id SERIAL PRIMARY KEY,
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
     agent_id VARCHAR(32) UNIQUE NOT NULL,
     agent_name VARCHAR(255),
     architecture VARCHAR(10) NOT NULL,
     system VARCHAR(10) NOT NULL,
     hostname VARCHAR(100) NOT NULL,
     version VARCHAR(10) NOT NULL,
-    capabilities JSON,
-    registered_at timestamp without time zone DEFAULT now() NOT NULL
+    capabilities TEXT,
+    registered_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP NOT NULL
 );
 
 CREATE UNIQUE INDEX idx_agent_id ON agents (id);
-CREATE UNIQUE INDEX idx_agent_id_id On agents (agent_id)
+CREATE UNIQUE INDEX idx_agent_id_id ON agents (agent_id);