List, assign, and resolve TeamCity investigations

### Area

Build Operations (run, trigger, cancel, logs)

### Problem or use case

Users need to inspect assigned TeamCity investigations from the terminal and may need to assign or resolve them. This concerns TeamCity investigation records, separate from AI failure diagnosis in #283.

### Proposed solution

First establish demand for a read-only list/view workflow, scoped by project or assignee, with JSON output. `/app/rest/investigations` responds successfully on cli.teamcity.com; there were no records to verify populated output.

Assignment and resolution should be a separate slice. Define how callers identify tests versus build problems, handle ambiguous names and permissions, and choose the investigation scope. Verify reads with real records and writes with disposable Sandbox records before claiming support.

Command placement remains open; this issue does not require a new top-level noun.

### Alternatives considered

Use the TeamCity UI or `teamcity api` with the investigations endpoint until a dedicated workflow is justified.

### Contribution

- [ ] I'd be willing to submit a PR (once it's `status:finalized`)