SMITH-022 Implement test-controller presentation

[webfish0]

Outcome

Extensions can expose and run tests.

Scope

• Discovery hierarchy and incremental updates.
• Run/debug profiles, status, duration, output, and source navigation.
• Failure messages and terminal-safe diffs.
• Reconnect and cancellation behavior.

Acceptance criteria

• T-018 and test cases in T-019 pass with a real controller.

Requirements: US-007, FR-010, FR-012

Source: backlog.md SMITH-022.