fix(tui): make playbook templates keyboard accessible

[edwin-zvs]

Fixes #1099.

Summary

• add visible ↑/↓ or C-p/C-n select · Enter apply keyboard affordance to the empty Playbook template list
• render each template's daemon-provided description beneath its name, matching the web UI
• keep the full name+description row mouse-activatable
• update spec 0049 with the keyboard and description semantics

Verification

• cargo check -p construct-cli
• cargo test -p construct-cli playbook_empty_template -- --nocapture (2 passed)
• cargo test -p construct-cli playbook_empty_placeholder -- --nocapture (9 passed)
• cargo build
• full cargo test -p construct-cli: 1,395 passed; color::tests::truecolor_backend_still_emits_rgb fails identically on untouched main in this environment

Demo

After-only recording captured from the worktree binary. It opens an empty Playbook, shows descriptions + key hint, focuses Goal with C-n, and applies it with Enter.

[edwin-zvs]

After-only TUI demo: descriptions and the visible keyboard hint appear in the empty Playbook; Down focuses Goal and Enter applies it.\n\n

[edwin-zvs]

Updated after-only demo: the empty Playbook advertises ↑/↓ or C-p/C-n select · Enter apply; this recording uses C-n to focus Goal and Enter to apply it.\n\n