cameras: split camera enable (Вкл) from REC (record-to-disk)

Add a separate `record` field so a camera can be registered but fully
off, or on but not recording:
- enabled (Вкл): camera on/off. Disabled = no go2rtc stream (no live),
  no recording; entry is just stored. build_streams/sync_all/reconcile
  skip disabled cameras; live grid shows "камера выключена".
- record (REC): write segments to disk. Recorder runs only when
  enabled AND record.

Unified POST /api/cameras/{id}/toggle {enabled?, record?} (replaces the
/record endpoint); go2rtc is touched only when `enabled` changes, so
flipping REC doesn't blip live. Camera table gets Вкл + Запись toggle
columns; add/edit forms get both switches.

load_config migrates the old schema (no `record` key): old `enabled`
meant "record" with live always on -> enabled=True, record=old enabled.

VERSION -> 0.0.126.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/settings.html

@@ -55,7 +55,7 @@
           </div>
           <table class="cams">
             <thead>
-              <tr><th style="width:48px">ID</th><th>Камера</th><th>IP</th><th>Потоки</th><th style="width:72px">Запись</th><th>Статус</th><th></th></tr>
+              <tr><th style="width:48px">ID</th><th>Камера</th><th>IP</th><th>Потоки</th><th style="width:56px">Вкл</th><th style="width:64px">Запись</th><th>Статус</th><th></th></tr>
             </thead>
             <tbody id="cam-rows"></tbody>
           </table>