feat: Add interactive mode to --tree UI with keyboard navigation

[Copilot]

Adds interactive keyboard-driven mode to --tree UI for post-run test exploration and selective re-runs.

Changes

TreeViewDisplay.cs (+202 lines)

• IsExpanded property on TreeViewNode for collapse/expand state tracking
• Selection state: _selectedIndex, _interactiveMode fields
• Navigation: SelectUp(), SelectDown() with auto-scroll
• Toggle: ToggleSelectedNode() rebuilds flattened view
• Re-run support: GetSelectedNodeTests() recursively collects test FQNs
• Visual indicators: > (selection), ▼/▶ (expand/collapse), help footer

TestRunner.cs (+134 lines)

• RunInteractiveModeAsync() orchestrates keyboard loop and re-run workflow
• Checks Console.IsInputRedirected to skip when stdin redirected (CI/CD)
• Handles keys: ↑/↓ (navigate), Enter (toggle), 'r' (re-run), Ctrl+C (exit)
• After re-run completes, returns to interactive mode with updated results

Behavior

╭─MyTests (15/15)────────────────────────────────────────╮
│ 15 passed  0 failed  00:00                             │
│ ████████████████████████████████████████████████ 100 % │
│                                                         │
│ > └─ ▼ ● Asynkron (15/15)      ← selected              │
│      └─ ▼ ● TestRunner (15/15)                         │
│         └─ ● Tests (15/15)                              │
│                                                         │
│ ↑↓ navigate | Enter expand/collapse | r re-run         │
╰─────────────────────────────────────────────────────────╯

Press 'r' on a failed branch to re-run just those tests. Repeat until done. Ctrl+C to exit.

Original prompt

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This section details on the original issue you should resolve

<issue_title>feat: Add interactive mode to --tree UI with keyboard navigation</issue_title>
<issue_description>## Summary

Add interactive keyboard-driven mode to the --tree UI that allows users to navigate and manipulate the test tree after the initial test run completes.

Features

• Keyboard Navigation: Use up/down arrow keys to navigate the tree
• Expand/Collapse: Press Enter to expand or collapse tree nodes
• Re-run Tests: Press 'r' to re-run the selected branch (and all tests within it)
• Persistent UI: No final summary screen; UI continues accepting input until the user initiates a re-run
• Continuous Input: After a re-run completes, the UI returns to interactive mode with updated results

Behavior

1. After test run completes, display the tree in interactive mode
2. User navigates using keyboard (↑/↓ to select nodes)
3. Pressing Enter toggles expand/collapse on the selected node
4. Pressing 'r' re-runs all tests in the selected branch
5. After re-run, tree updates with new results and returns to interactive mode
6. Loop continues until user exits (e.g., Ctrl+C)

Implementation Notes

• Extend ChartRenderer.cs or create new InteractiveTreeRenderer
• Integrate with TestRunner.cs or create InteractiveRunner.cs
• Track selected node position in tree
• Support filtering re-run logic to only selected branch and children
• Consider visual indicator for currently selected node
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes feat: Add interactive mode to --tree UI with keyboard navigation #13

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