refactor: consolidate hooks table migration and drop deprecated agent_id column

- Consolidated PG migration 054: agent_hooks rename + junction table + deprecated column drop
- Updated SQLite schema v19 with final consolidated migration
- Removed obsolete schema rebuild files (v21, v23)
- Updated Go store layer (pg/hooks.go, sqlitestore/hooks.go)
- Updated integration tests to use new table names (hooks, hook_agents)
- Updated TypeScript protocol, UI components, and i18n strings
- Updated gateway methods to reflect schema changes

Tables: agent_hooks → hooks, agent_hook_agents → hook_agents

internal/store/sqlitestore/schema.sql

@@ -1570,18 +1570,14 @@ CREATE INDEX IF NOT EXISTS idx_vault_links_source
     WHERE json_extract(metadata, '$.source') IS NOT NULL;
 
 -- ============================================================
--- Table: agent_hooks (migrations 000052 + 000053)
+-- Table: hooks (renamed from agent_hooks, migration 000055)
 -- SQLite translation: JSONB→TEXT, TIMESTAMPTZ→TEXT, UUID→TEXT,
 -- BYTEA→BLOB, DATE→TEXT (ISO8601), CHECK for enums.
--- v21 (migration 000053): handler_type adds 'script', source adds 'builtin',
--- old (event, handler_type) uniqueness indexes dropped — scripts routinely
--- want many small hooks per event.
 -- ============================================================
 
-CREATE TABLE IF NOT EXISTS agent_hooks (
+CREATE TABLE IF NOT EXISTS hooks (
     id           TEXT NOT NULL PRIMARY KEY,
     tenant_id    TEXT NOT NULL DEFAULT '0193a5b0-7000-7000-8000-000000000001',
-    agent_id     TEXT REFERENCES agents(id) ON DELETE CASCADE,
     scope        TEXT NOT NULL CHECK (scope IN ('global', 'tenant', 'agent')),
     event        TEXT NOT NULL,
     handler_type TEXT NOT NULL CHECK (handler_type IN ('command', 'http', 'prompt', 'script')),
@@ -1602,16 +1598,29 @@ CREATE TABLE IF NOT EXISTS agent_hooks (
 );
 
 CREATE INDEX IF NOT EXISTS idx_hooks_lookup
-    ON agent_hooks (tenant_id, agent_id, event)
+    ON hooks (tenant_id, event)
     WHERE enabled = 1;
 
+-- ============================================================
+-- Table: hook_agents (renamed from agent_hook_agents, N:M junction)
+-- ============================================================
+
+CREATE TABLE IF NOT EXISTS hook_agents (
+    hook_id  TEXT NOT NULL REFERENCES hooks(id) ON DELETE CASCADE,
+    agent_id TEXT NOT NULL REFERENCES agents(id) ON DELETE CASCADE,
+    PRIMARY KEY (hook_id, agent_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_hook_agents_agent
+    ON hook_agents (agent_id);
+
 -- ============================================================
 -- Table: hook_executions (append-only audit log, migration 000052)
 -- ============================================================
 
 CREATE TABLE IF NOT EXISTS hook_executions (
     id           TEXT NOT NULL PRIMARY KEY,
-    hook_id      TEXT REFERENCES agent_hooks(id) ON DELETE SET NULL,
+    hook_id      TEXT REFERENCES hooks(id) ON DELETE SET NULL,
     session_id   TEXT,
     event        TEXT NOT NULL,
     input_hash   TEXT,