test: Add test coverage for untested core files

[nigel-dev]

Description

Five core source files have zero test coverage. These files handle slash commands, tool registration, data directories, status reporting, and the dashboard — all user-facing functionality.

Untested Files

File	Lines	Responsibility	Risk
`src/commands.ts`	~170	All slash command registration and dispatch	Medium — user-facing
`src/tools/overview.ts`	~200	`mc_overview` dashboard aggregation	Medium — primary status tool
`src/tools/report.ts`	~69	`mc_report` agent status reporting	High — agent communication
`src/lib/paths.ts`	~30	Data directory resolution	Low — simple but foundational
`src/lib/orchestrator-singleton.ts`	~40	Shared orchestrator/monitor instances	Medium — state management

Proposed Approach

`commands.ts` (good starting point)

• Test that each slash command dispatches to the correct tool
• Test argument parsing (e.g., `/mc-status jobname` extracts `jobname`)
• Test error handling for missing arguments

`overview.ts`

• Test dashboard output format with various job states
• Test with no jobs, running jobs, failed jobs, active plan
• Test suggested actions logic

`report.ts`

• Test `isInManagedWorktree` detection
• Test report writing with various statuses
• Test error when called from non-managed worktree

`paths.ts`

• Test data directory resolution
• Test project identification

`orchestrator-singleton.ts`

• Test singleton pattern (same instance returned)
• Test set/get for orchestrator and monitor

How to Verify

```bash
bun test
```

All new tests should follow existing patterns in `tests/` — see `tests/tools/cleanup.test.ts` or `tests/hooks/notifications.test.ts` for good examples of the mocking style used.

Additional Context

From audit report Section 7 (Test Coverage Gaps): "Untested: commands.ts, index.ts, paths.ts." The explore agent confirmed overview.ts, report.ts, and orchestrator-singleton.ts are also uncovered.