fix(clip): typed times belong to their value, and every mark on the player chrome can be seen

TimecodeField drops a draft when the value moves under it (another segment selected, a nudge), so
leaving the field never commits it to another cut; it is invalid only once offered, with a line
under it saying how to type a time. On the always-dark chrome media-scope points every focus ring
at --media-mark and errors at the new --media-danger (a light theme's accent and danger were under
3:1 there). A track whose dragged handle unmounts ends the drag on the pointer's release instead of
locking up; a remove refused while clips are queued leaves no focus to take later; each remove-cut
button names its cut and is a 24px target. DESIGN.md records the media tokens; stale comments fixed.

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

@@ -2,6 +2,8 @@
   "privacyPolicy": "Privacy policy",
   "termsOfService": "Terms of service",
   "sourceCode": "Source code",
+  "timecodeInvalid": "Not a time — type it like 1:05.5",
+  "timecodeInvalidHours": "Not a time — type it like 1:02:05.5",
   "close": "Close",
   "cancel": "Cancel",
   "confirm": "Confirm",