Add fullscreen crop mode toggle (hotkey c)

- In fullscreen, press 'c' to toggle object-fit between contain (default)
  and fill (stretches to fill, no aspect ratio preservation).
- Adds .player.crop-mode video { object-fit: fill; } in player.css.
- Adds toggleCrop() in player.js that toggles a crop-mode class and a
  small UI indicator (✂️) in the controls, visible only in fullscreen.
- Resets crop mode back to contain when exiting fullscreen (via Escape,
  minimize, or fullscreenchange event).
- Wires the 'c' hotkey in keyboard.js and registers toggleCrop in app.js.
- Adds crop-indicator to index.html and detach.html controls, and
  documents the shortcut in the help modal.

1 files changed, 2 insertions, 0 deletions

diff --git a/web/index.html b/web/index.html
index f3e37a1..4b90f92 100644
--- a/web/index.html
+++ b/web/index.html
@@ -90,6 +90,7 @@
       <input id="volume-slider" type="range" min="0" max="1" step="0.05" value="1" class="volume-slider" aria-label="Volume">
     </div>
     <button id="btn-fullscreen" class="icon-btn" aria-label="Fullscreen (f)">⛶</button>
+    <span id="crop-indicator" class="crop-indicator hidden" title="Crop mode active (c)">✂️</span>
   </div>
   <button id="btn-restore-player" class="player-restore" type="button" aria-label="Restore player">
     <span id="player-restore-title">Player minimized</span>
@@ -133,6 +134,7 @@
         <div class="help-row"><span><kbd>S</kbd></span><span>Share selected media</span></div>
         <div class="help-row"><span><kbd>+</kbd> <kbd>−</kbd></span><span>Zoom in / out (image viewer)</span></div>
         <div class="help-row"><span><kbd>Shift+S</kbd></span><span>Toggle slideshow (images)</span></div>
+        <div class="help-row"><span><kbd>c</kbd></span><span>Toggle crop mode (fullscreen)</span></div>
         <div class="help-row"><span><kbd>L</kbd></span><span>My Shares</span></div>
         <div class="help-row"><span><kbd>?</kbd></span><span>Show / hide help</span></div>
       </div>