Contraction: remove the TUI's origins group #418

The TUI's origins group is gone and the branch is pushed. The full forge.json check was not run. I ran the TUI suites (tui-workflows, tui-code) and tsc --noEmit, and they pass. An earlier run of the TUI suites plus web.test.ts showed 3 failures, all in the origin-driven tui-workflows tests I then removed. I did not re-run web.test.ts after that.

What changed

• Removed the screen and its entry points. src/tui/screens/origins.ts (1030 lines) is deleted. So are its palette entry in src/tui/forge.ts, the o key in src/tui/screens/account.ts and its help-bar hints.
• Dropped the TUI origins tests. I deleted test/tui-origins.test.ts. I also removed the "workflows at an origin" describe from test/tui-workflows.test.ts, which could only be reached through the deleted picker.
• Docs. docs/DESIGN.md now says origins are web-only (/origins and migrate). It no longer lists the origins list or the origin picker among the clickable surfaces. docs/STUDIO.md never mentioned the TUI origins group, so it needed no change.
• Line count. The change deletes 2288 lines and adds 8.

Choices to check

• Old URLs. No web route was touched, so every old URL answers as before. No TUI route existed, so there is nothing to redirect and no per-route test to add.
• Lost coverage. The deleted workflow tests covered fork-at-origin (F), propose-upstream and the ordinary commit dialog on a pushable repo, all through the TUI. Those paths are no longer tested through the terminal. The underlying actions keep their own tests (test/forks.test.ts, test/cross-repo-pull.test.ts, test/web.test.ts).
• Left alone. src/tui/screens/contribute.ts and the F key code may now have no entry point in the TUI. I did not prune them. A follow-up could check for dead code.
• Left untouched. The release workflow and the chart.

To try it

• Run bun run src/main.ts.
• Open the terminal. Account no longer offers o, and the palette has no "Origins".
• On the web, /origins and migrate work as before.

🤖 Generated with Claude Code

Closes #399