feat: Agent System Prompts MVP (B) - database, backend API, and frontend integration

migrations/040_agent_prompts.sql

@@ -0,0 +1,23 @@
+-- Create agent_prompts table
+CREATE TABLE IF NOT EXISTS agent_prompts (
+    id text PRIMARY KEY DEFAULT ('ap_' || substr(md5(random()::text), 1, 12)),
+    agent_id text NOT NULL REFERENCES agents(id) ON DELETE CASCADE,
+    kind text NOT NULL CHECK (kind IN ('core', 'safety', 'governance', 'tools')),
+    content text NOT NULL,
+    version integer NOT NULL DEFAULT 1,
+    created_at timestamptz NOT NULL DEFAULT NOW(),
+    updated_at timestamptz NOT NULL DEFAULT NOW(),
+    created_by text,
+    note text,
+    is_active boolean NOT NULL DEFAULT true
+);
+
+-- Create indexes
+CREATE UNIQUE INDEX IF NOT EXISTS ux_agent_prompts_agent_kind_version ON agent_prompts(agent_id, kind, version);
+CREATE INDEX IF NOT EXISTS ix_agent_prompts_agent_id ON agent_prompts(agent_id);
+CREATE INDEX IF NOT EXISTS ix_agent_prompts_agent_kind_active ON agent_prompts(agent_id, kind) WHERE is_active = true;
+
+-- Grant permissions (adjust based on your RBAC)
+GRANT ALL ON agent_prompts TO postgres;
+-- GRANT SELECT, INSERT, UPDATE ON agent_prompts TO app_user; -- Uncomment if needed
+