Fix session UNIQUE constraint race, fix table horizontal scrollbar

- create_session uses INSERT OR IGNORE to handle concurrent requests
  with same session cookie (race when multiple requests arrive before
  the first INSERT commits)
- Widen actions column 110px→130px to fit 3 action buttons without
  overflowing (was causing 4px horizontal scrollbar)
- Widen status column 100px→120px for DOWNLOADING badge breathing room

backend/app/core/database.py

@@ -319,10 +319,10 @@ async def close_db(db: aiosqlite.Connection) -> None:
 
 
 async def create_session(db: aiosqlite.Connection, session_id: str) -> None:
-    """Insert a new session row."""
+    """Insert a new session row (idempotent — ignores duplicates)."""
     now = datetime.now(timezone.utc).isoformat()
     await db.execute(
-        "INSERT INTO sessions (id, created_at, last_seen) VALUES (?, ?, ?)",
+        "INSERT OR IGNORE INTO sessions (id, created_at, last_seen) VALUES (?, ?, ?)",
         (session_id, now, now),
     )
     await db.commit()

frontend/src/components/DownloadTable.vue

@@ -387,11 +387,11 @@ a.name-with-icon:hover .name-text {
   min-width: 0;
 }
 
-.col-status { width: 100px; }
+.col-status { width: 120px; white-space: nowrap; }
 .col-progress { width: 180px; min-width: 120px; }
 .col-speed { width: 100px; }
 .col-eta { width: 80px; }
-.col-actions { width: 110px; }
+.col-actions { width: 130px; }
 
 /* Status badges */
 .status-badge {