fix: preserve terminal stderr for ticket pickers

[dkarter]

Motivation

Interactive ticket pickers can render a blank screen because HWT turns stderr into a pipe. Preserve terminal stderr so pickers work without a 2>/dev/tty shell wrapper.

Summary of changes

• Pass terminal stderr directly to the command; keep stdout reserved for JSON.
• Keep streaming and captured diagnostics for redirected stderr and injected writers.
• Add real Bubble Tea PTY regression tests and an end-to-end branch/metadata test.

Testing

To verify manually, configure a picker as direct argv, such as [lnr, issue, search, --json, '{input}'], and run hwt create --ticket --json in Herdr. Confirm the picker renders, Enter creates the selected branch with ticket metadata, and Escape cancels without creating a worktree. Redirect stdout to a file to confirm no UI appears in the JSON.

Verified in a live Herdr pane with fake ticket data and a disposable repository: the picker received real dimensions, Enter created a real Herdr workspace/worktree, metadata persisted, and Escape preserved the picker exit status. Test workspace and pane were removed.

Also passed the full mise run check, 20 repeated macOS race-enabled ticket-command test runs, 20 repeated Linux container test runs, and 10 repeated ticket E2E runs.

Dependencies/special considerations

• Adds github.com/creack/pty for tests and uses the existing cross-platform terminal library directly.
• Windows build remains blocked by pre-existing Unix-only Flock calls in internal/localdns/localdns.go.
• Existing user shell workarounds remain untouched until the native fix is released and installed.

[pullfrog]

✅ No new issues found.

Reviewed changes Reviewed all seven changed files, including subprocess descriptor handling, failure diagnostics, and the terminal regression tests.

• Terminal inheritance: Ticket commands receive terminal stderr directly, preserving terminal identity and dimensions while stdout remains reserved for JSON.
• Diagnostic handling: Redirected stderr and injected writers retain streaming and capture; terminal failures avoid repeating unrelated stdout and preserve wrapped subprocess errors.
• Regression coverage: Real Bubble Tea PTY tests exercise selection and cancellation, and a hermetic CLI test verifies branch creation and persisted ticket metadata. The specification and dependencies reflect the new coverage.

Verification passed on Linux: mise exec -- go test ./..., mise exec -- go vet ./..., and five race-enabled repetitions of the ticket-command tests. macOS and live Herdr behavior were not independently exercised during this review.

  ^{｜ View workflow run ｜ Using gpt-6.1-sol ｜ 𝕏}