Dashboard terminal recording support with manual controls and extensible recorder API

## Feature request
Add first-class terminal session recording support in the Aspire dashboard, backed by the existing Hex1b asciinema recording capability.

## User experience goal
Provide built-in manual controls in the dashboard to:
1. Start recording from the terminal UI.
2. Stop recording.
3. Download/save the resulting recording file locally.

## Why this is useful
- Makes it easier to file actionable bugs for terminal emulation issues.
- Helps users capture/share sessions for their own troubleshooting and demos.

## API direction
Consider introducing an `ITerminalRecorder` API (via DI) so apps/extensions can programmatically trigger recordings in addition to manual UI controls.

## Design considerations
- Keep room in the API/model for multiple recordings per session/resource.
- Track prior recordings for potential future dashboard features like selection/playback.
- Consider integration points with telemetry download workflows.

## Scope notes
- Manual start/stop/download in dashboard should be built-in.
- Programmatic triggering via DI should be extensible without requiring dashboard UI customization.

## Backlog
Track as backlog work.