feat(player): clip mode - mark a range of what is playing and cut it into a download

Both players get a scissors in their control row (Plex: the control row; YouTube: the actions and
the docked bar), `c`, and `[` / `]` to mark at the playhead. The clip panel lives in the player, so
the watched video is the preview: an overview of the whole item and a zoomed strip around the
selection whose ends are sliders (arrows step a tenth, Shift a second), Start / End fields with
nudges and "to the playhead", the length, a looping Play selection, a name, Cut. Escape closes the
panel before the player and the focus goes back to the scissors. A cut is a toast with a Downloads
link plus the usual Ready notification.

- ui/RangeTrack + RulerTicks: the shared, domain-free time track (regions, keyboard-steppable
  handles with a 1.5rem hit area, a playhead, a background slot, over a window of the item). The
  Downloads editor's cuts moved onto it, so they are keyboard-steppable now.
- lib/clipRange holds the marking rules (1 s to 10 min, the server's), lib/timecode the editing
  timecode the editor's private tc/parseTc became.
- keymap: a symbol typed through AltGr answers its bare-symbol row - on the HU layout `[` is
  AltGr+F, which arrives as Ctrl+Alt; letter and Mod rows still never match Ctrl+Alt.
- The YouTube stage sits in a wrapper with the panel, so the maximised stage's blur escape matches
  at any depth.
- media-scope: fields on the always-dark player chrome read white in a light theme too.

frontend/src/i18n/locales/en/clip.json

@@ -0,0 +1,21 @@
+{
+  "title": "Clip",
+  "open": "Make a clip",
+  "close": "Close the clip panel",
+  "overview": "Whole video",
+  "strip": "Clip range",
+  "in": "Start",
+  "out": "End",
+  "inHere": "Start at the current position",
+  "outHere": "End at the current position",
+  "earlier": "{{label}}: a tenth of a second earlier",
+  "later": "{{label}}: a tenth of a second later",
+  "length": "Length {{length}}",
+  "loop": "Play selection",
+  "name": "Clip name",
+  "namePlaceholder": "Clip name (optional)",
+  "cut": "Cut clip",
+  "queued": "The clip is being made — it will be in your downloads",
+  "view": "Downloads",
+  "failed": "Couldn’t make the clip"
+}

frontend/src/i18n/locales/en/editor.json

@@ -39,5 +39,7 @@
   "droppedSeg": "Dropped segment",
   "removeCut": "Remove cut",
   "keptSummary": "{{n}} kept · {{dur}}",
-  "createJoin": "Create joined clip"
+  "createJoin": "Create joined clip",
+  "timeline": "Timeline",
+  "cutN": "Cut {{n}}"
 }

frontend/src/i18n/locales/en/keys.json

@@ -38,5 +38,7 @@
   "cap": {
     "space": "Space",
     "menu": "Menu"
-  }
+  },
+  "clip": "Clip mode",
+  "clipMark": "Mark the clip’s start / end here"
 }

frontend/src/i18n/locales/hu/clip.json

@@ -0,0 +1,21 @@
+{
+  "title": "Klip",
+  "open": "Klip készítése",
+  "close": "Klippanel bezárása",
+  "overview": "A teljes videó",
+  "strip": "A klip tartománya",
+  "in": "Eleje",
+  "out": "Vége",
+  "inHere": "Eleje a mostani pozíciónál",
+  "outHere": "Vége a mostani pozíciónál",
+  "earlier": "{{label}}: egy tized másodperccel korábban",
+  "later": "{{label}}: egy tized másodperccel később",
+  "length": "Hossz {{length}}",
+  "loop": "Kijelölés lejátszása",
+  "name": "A klip neve",
+  "namePlaceholder": "A klip neve (nem kötelező)",
+  "cut": "Klip vágása",
+  "queued": "Készül a klip — a letöltéseid közé kerül",
+  "view": "Letöltések",
+  "failed": "Nem sikerült elkészíteni a klipet"
+}

frontend/src/i18n/locales/hu/editor.json

@@ -39,5 +39,7 @@
   "droppedSeg": "Eldobott szegmens",
   "removeCut": "Vágás törlése",
   "keptSummary": "{{n}} megtartva · {{dur}}",
-  "createJoin": "Összefűzött klip"
+  "createJoin": "Összefűzött klip",
+  "timeline": "Idővonal",
+  "cutN": "{{n}}. vágás"
 }

frontend/src/i18n/locales/hu/keys.json

@@ -38,5 +38,7 @@
   "cap": {
     "space": "Szóköz",
     "menu": "Menü"
-  }
+  },
+  "clip": "Klip mód",
+  "clipMark": "A klip eleje / vége itt"
 }