ci: add health endpoint, safety-load mock data, update README + screenshot

[OneByJorah]

Summary

• Adds a `/health` endpoint for monitoring and deploy hooks.
• Makes mock-data loading resilient to missing / malformed JSON files.
• Loads data via `file`-relative path so cwd moves do not break the app.
• Replaces README screenshot asset with a live local render.
• Documented stack manifest and reviewer findings.

Deploy status

• Before: app crashes if `mock_dc_status.json` is missing; no health endpoint.
• After: safe defaults on missing data; `/health` returns `{"status":"ok"}`.

Findings fixed

• ADS-001: explicit error handling for missing/malformed data file.
• ADS-002: new `/health` endpoint.
• ADS-003: path-relative data lookup.

Open / needs human review

• None.

Models used:

• Writer/subagent: ornith:9b