TUI polish: alternate screen, safe actions, detail panel, log viewer

[chanakyav]

Summary

Major TUI polish: alternate screen buffer, safe actions, detail panel, built-in log viewer. Closes #11.

Alternate Screen Buffer

• Uses ESC[?1049h / ESC[?1049l to isolate the TUI from terminal scrollback history
• Previous renders are no longer visible when scrolling up — the dashboard is a clean, stable screen
• Cursor hidden during TUI, always restored in a finally block

HEAVY Borders + Row Padding

• Switched from ROUNDED to HEAVY box style — thick borders that pop on dark terminals
• Added vertical padding between rows for visual breathing room
• Session count shown in title: "Sessions (3)"

Safe Action Handlers

Every keybinding action catches errors and shows a temporary status message instead of crashing:

• Enter on a dead session → "Session not running — task is COMPLETE"
• x on a completed task → "Already complete"
• tmux not available → "tmux not available"
• os.execvp completely removed — all tmux operations use subprocess.run
• Status messages auto-clear after 3 seconds

Detail Panel (d / Space)

Split-pane preview showing task metadata + log tail:

• Branch, state, PR, iteration, elapsed time
• Last 8 lines from orchestrator.log (live tail)
• Table switches to compact mode when panel is open
• Press d again or Esc to close

Log Viewer (l)

Full-screen scrollable log viewer:

• j/k to scroll, G to jump to end, g to jump to top
• Auto-refreshes log content on timeout (catches new lines from active tasks)
• Position indicator: "Line 45-80 of 120"
• q/Esc returns to session list

Dynamic Footer

Changes based on current view mode:

• Main: j/k navigate Enter attach x stop l logs d detail r refresh q quit
• Detail: j/k navigate d close detail l full logs q quit
• Logs: j/k scroll G end g top q back

Tests

• 39 new tests in test_dashboard.py covering:
  • Spinner animation cycling for all working/waiting states
  • Table building with selection, compact mode, long branch truncation
  • Detail panel rendering with/without PR
  • Log tail reading from disk
  • All footer builders
  • Status message rendering
  • Key reading with deterministic pipe-based input simulation (all 14 key bindings)
• 136 tests total, all passing, ruff clean

Docs Updated

• README: Full keybinding tables for session list view and log viewer
• copilot-instructions: Added TUI safety conventions (no execvp, alternate screen, finally blocks)