fix: single-key TTY menu UX for the Gitea config menu (#36)

Make the interactive profile menu feel like a real terminal menu, via a new
injectable MenuIO abstraction (no menu logic change, no auth/secret-storage
change).

- Single-key top-level actions in a TTY (termios/tty raw read); no Enter
  needed. Non-TTY / test runs fall back to line input.
- Enter backs out: Enter (or 0) on the main menu quits; Enter cancels any
  submenu/profile prompt and returns.
- Profile chooser: everywhere a profile is needed, show a numbered list and
  pick by key (1-9), with an explicit 'm) type a name manually' path and Enter
  to cancel. Empty config handled gracefully.
- Clear screen before redrawing the main menu and chooser — TTY only; never
  emits clear codes in non-TTY/test runs.
- Result actions (validate/test-auth/whoami/eligibility) print a concise result
  then pause for a keypress in a TTY; non-TTY never blocks.

Helpers: read_key (via default_io) / choose_menu_option / choose_profile /
clear_screen / pause_for_key, plus MenuIO(is_tty, clear_enabled). TTY detected
with sys.stdin.isatty() and sys.stdout.isatty(); stdlib only.

Safety unchanged: no tokens/passwords printed, no raw config dumps, no
.env.personal, no change to auth behavior or secret storage.

Tests: rewrote menu tests around a scripted _FakeIO (no real terminal): single-
key select + clear, main-menu Enter/0 quit, submenu Enter cancel (no change),
chooser lists/selects/no-profiles/manual/out-of-range, non-TTY line fallback,
clear-only-when-enabled, pause never hangs non-TTY, and add-flow proving the
token value never reaches disk or stdout.

Docs: runbook note on single-key nav / Enter back-out / numbered chooser.
scripts/gitea-config-menu unchanged.

Closes #36. Refs #31, #34.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/llm-workflow-runbooks.md

@@ -115,6 +115,11 @@ Menu options: list / add / edit / remove profiles · validate config · test
 profile authentication · show authenticated user · generate launcher snippets
 (Claude/Gemini/Codex) · check reviewer eligibility for a PR.
 
+In a real terminal the menu takes a **single keypress** (no Enter), **Enter**
+quits the main menu and cancels/back-outs of any submenu, and you pick a profile
+from a **numbered list** instead of typing its name. Non-interactive runs
+(pipes/tests) fall back to line input and never block.
+
 **Create an author + a reviewer profile:**
 
 1. `add profile` → name `prgs-author`, base URL, username, default owner/repo,