Phase 3 : chat streaming SSE et persistance des sessions

Backend :
- db.py : SQLite (sessions + messages), schéma et CRUD
- routes/sessions.py : créer/lister/ouvrir/renommer/supprimer une session
- routes/chat.py : POST /api/chat, relais token par token depuis Ollama (SSE),
  persistance des messages, titrage auto de la session au 1er message
- main.py : lifespan -> init_db, montage des nouvelles routes

Frontend :
- api/client.ts : APIs sessions + streamChat (parsing SSE event/data)
- store : sessions, messages, état de streaming, envoi optimiste
- ChatPanel : fil de conversation réel, bulles user/agent, curseur de frappe
- LeftPanel : historique réel (ouvrir/supprimer, horodatage relatif)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SVay7z3y7q2gEe54ByAE6N

backend/app/db.py

@@ -0,0 +1,135 @@
+"""Persistance SQLite : sessions et messages.
+
+On utilise sqlite3 de la bibliothèque standard (zéro dépendance). Les écritures
+sont rapides ; un verrou protège l'accès concurrent depuis les routes async.
+"""
+from __future__ import annotations
+
+import os
+import sqlite3
+import threading
+import time
+import uuid
+
+from .config import settings
+
+_LOCK = threading.Lock()
+_DB_PATH = os.path.join(settings.data_dir, "loki.db")
+
+
+def _connect() -> sqlite3.Connection:
+    os.makedirs(settings.data_dir, exist_ok=True)
+    conn = sqlite3.connect(_DB_PATH, check_same_thread=False)
+    conn.row_factory = sqlite3.Row
+    return conn
+
+
+def init_db() -> None:
+    """Crée les tables si elles n'existent pas."""
+    with _LOCK, _connect() as conn:
+        conn.executescript(
+            """
+            CREATE TABLE IF NOT EXISTS sessions (
+                id          TEXT PRIMARY KEY,
+                title       TEXT NOT NULL,
+                model       TEXT,
+                created_at  REAL NOT NULL,
+                updated_at  REAL NOT NULL
+            );
+            CREATE TABLE IF NOT EXISTS messages (
+                id          TEXT PRIMARY KEY,
+                session_id  TEXT NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
+                role        TEXT NOT NULL,
+                content     TEXT NOT NULL,
+                model       TEXT,
+                created_at  REAL NOT NULL
+            );
+            CREATE INDEX IF NOT EXISTS idx_messages_session
+                ON messages(session_id, created_at);
+            """
+        )
+
+
+def _now() -> float:
+    return time.time()
+
+
+# ── Sessions ─────────────────────────────────────────────────────────────
+def create_session(title: str, model: str | None) -> dict:
+    sid = uuid.uuid4().hex
+    now = _now()
+    with _LOCK, _connect() as conn:
+        conn.execute(
+            "INSERT INTO sessions (id, title, model, created_at, updated_at)"
+            " VALUES (?, ?, ?, ?, ?)",
+            (sid, title, model, now, now),
+        )
+    return {"id": sid, "title": title, "model": model,
+            "created_at": now, "updated_at": now, "message_count": 0}
+
+
+def list_sessions() -> list[dict]:
+    with _LOCK, _connect() as conn:
+        rows = conn.execute(
+            """
+            SELECT s.*, COUNT(m.id) AS message_count
+            FROM sessions s
+            LEFT JOIN messages m ON m.session_id = s.id
+            GROUP BY s.id
+            ORDER BY s.updated_at DESC
+            """
+        ).fetchall()
+    return [dict(r) for r in rows]
+
+
+def get_session(sid: str) -> dict | None:
+    with _LOCK, _connect() as conn:
+        row = conn.execute("SELECT * FROM sessions WHERE id = ?", (sid,)).fetchone()
+    return dict(row) if row else None
+
+
+def rename_session(sid: str, title: str) -> None:
+    with _LOCK, _connect() as conn:
+        conn.execute(
+            "UPDATE sessions SET title = ?, updated_at = ? WHERE id = ?",
+            (title, _now(), sid),
+        )
+
+
+def delete_session(sid: str) -> None:
+    with _LOCK, _connect() as conn:
+        conn.execute("DELETE FROM messages WHERE session_id = ?", (sid,))
+        conn.execute("DELETE FROM sessions WHERE id = ?", (sid,))
+
+
+def touch_session(sid: str) -> None:
+    with _LOCK, _connect() as conn:
+        conn.execute(
+            "UPDATE sessions SET updated_at = ? WHERE id = ?", (_now(), sid)
+        )
+
+
+# ── Messages ─────────────────────────────────────────────────────────────
+def add_message(sid: str, role: str, content: str, model: str | None) -> dict:
+    mid = uuid.uuid4().hex
+    now = _now()
+    with _LOCK, _connect() as conn:
+        conn.execute(
+            "INSERT INTO messages (id, session_id, role, content, model, created_at)"
+            " VALUES (?, ?, ?, ?, ?, ?)",
+            (mid, sid, role, content, model, now),
+        )
+        conn.execute(
+            "UPDATE sessions SET updated_at = ? WHERE id = ?", (now, sid)
+        )
+    return {"id": mid, "session_id": sid, "role": role, "content": content,
+            "model": model, "created_at": now}
+
+
+def list_messages(sid: str) -> list[dict]:
+    with _LOCK, _connect() as conn:
+        rows = conn.execute(
+            "SELECT * FROM messages WHERE session_id = ? ORDER BY created_at",
+            (sid,),
+        ).fetchall()
+    return [dict(r) for r in rows]