Contract: the TUI's explore and owner screens leave, and its dashboard becomes a launcher #636

Pillar: P1 Feed (umbrella #587). Contract: one of the duplicated screens the studio/dev split left behind. One run, fresh from today's main.

The job: find a repository and open it in the TUI.

Survivor: the TUI dashboard as a short launcher: your repositories, the finder, open in the workspace or review. Browsing other people and forges is the web explorer's job (#607).

Removed in this same pull: src/tui/screens/explore.ts, src/tui/screens/owner.ts, and the dashboard's activity feed (the web feed's job), with their keys and tests.

The path: a developer connects over SSH to work on code; primary action open a repository in the workspace; next the workspace.

Acceptance.

• [ ] One renderer for this job, for every repository and every viewer; the other code and its tests are deleted, not hidden.
• [ ] Every old URL still answers (the survivor, or a redirect); ?mode=dev on it shows the survivor.
• [ ] Nothing the removed screen did is lost: the pull lists each thing it showed or did and where it lives now (or why nobody needs it).
• [ ] Minimal, not bare: one primary next action, white space at every width, nothing the person does not need now.
• [ ] Looks of the path at phone and desktop widths on the pull; the full check green.
• [ ] The TUI workspace, editor and review stay first-class over SSH and are untouched.

Start from: src/tui/screens/dashboard.ts, src/tui/screens/explore.ts, src/tui/screens/owner.ts, src/tui/screens/activity.ts.

Must not touch: the release workflow, the chart, other repositories.