docs(tui): move theme work to issue

specs/v2/tui-theme-migration.md

@@ -1,19 +0,0 @@
-# TUI Theme V2 Migration Checklist
-
-- [x] Add semantic accent foreground and border tokens so components stop
-      reading `hue.accent[300]` directly.
-- [ ] Add paired badge or label foreground/background tokens to replace V1
-      `secondary` usages.
-- [ ] Add strong warning and error background treatments with matching readable
-      foregrounds.
-- [x] Use `text.default` for active cursors, `background.surface.offset` for
-      disabled cursors, and a lighter accent hue for focused form borders.
-- [x] Add `background.surface.offset` and `background.surface.overlay`, map
-      them from V1 panel/menu backgrounds, and use them as contextual surface
-      defaults.
-- [ ] Replace `selectedForeground` with complete V2 foreground/background pairs
-      or a V2 contrast helper that supports transparent themes.
-- [ ] Decide whether thinking opacity is fixed at `0.6` or belongs in a separate
-      presentation-token system.
-- [ ] Generate syntax styles from resolved V2 tokens, then migrate each UI
-      surface and remove the V1 proxy once no flat V1 color reads remain.