feat(agent): v4.10.1 - config LLM dans l'UI (sélecteur provider/modèle, config runtime, admin + test connexion)

- Panneau agent : selects provider/modèles connus persistés par conversation
  (colonnes agent_conversations.provider/model, migration idempotente)
- GET /api/agent/providers enrichi (liste providers + modèles + requires_key)
- PATCH /api/agent/providers (admin) : config runtime DB-backed (table llm_config)
- POST /api/agent/providers/test : test connexion via LLMClient.ping() sans fallback mock
- Settings > Admin > Agent & IA : provider, modèle, clé API, URL API, save + test
- VERSION -> 4.10.1, CHANGELOG + ROADMAP mis à jour, 232 tests verts

app/db.py

@@ -726,6 +726,27 @@ def init_db():
         conn.execute("CREATE INDEX IF NOT EXISTS idx_agent_conv_user ON agent_conversations(user_id, updated_at)")
         conn.execute("CREATE INDEX IF NOT EXISTS idx_agent_msg_conv ON agent_messages(conversation_id, created_at)")
         conn.execute("CREATE INDEX IF NOT EXISTS idx_agent_action_conv ON agent_actions(conversation_id)")
+
+        # ─── v4.10.1: LLM runtime config (single row id=1) ─────────────────────
+        # Created lazily (no seed) so .env stays the default until an admin saves
+        # the LLM settings from the UI. Precedence: DB row > settings.llm_*.
+        conn.execute("""
+            CREATE TABLE IF NOT EXISTS llm_config (
+                id INTEGER PRIMARY KEY CHECK (id = 1),
+                provider TEXT NOT NULL DEFAULT 'offline',
+                model TEXT DEFAULT '',
+                api_key TEXT DEFAULT '',
+                api_base TEXT DEFAULT '',
+                updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+            )
+        """)
+        # Migration: per-conversation provider/model override columns
+        for col in ("provider", "model"):
+            try:
+                conn.execute(f"ALTER TABLE agent_conversations ADD COLUMN {col} TEXT DEFAULT ''")
+            except sqlite3.OperationalError:
+                pass  # column already exists
+        conn.execute("CREATE INDEX IF NOT EXISTS idx_agent_conv_llm ON agent_conversations(provider, model)")
         conn.commit()