Build G0 foundation and G1 read-only GUI

[miter37]

What changed

This branch publishes the completed G0 foundation and the first G1 read-only GUI implementation so development can continue from another machine.

• Adds versioned SQLite migration support and committed 0.5.0 database fixtures.
• Adds /health compatibility fields and read-only /v1/jobs APIs with search, filters, and cursor pagination.
• Adds request privacy/source metadata and the compatibility/agent registry foundations.
• Adds the optional PySide6 relay --gui client for Waiting, Running, Finished, Job Overview, filtering, date grouping, polling, reconnect handling, and compatibility read-only mode.
• Adds GUI optional dependencies and Windows/Ubuntu/macOS GUI smoke CI.
• Includes the v1.0, v1.2, and v1.3 GUI development plans.

Why

The next development phase needs a stable, portable baseline. This branch contains the local G0/G1 implementation and makes the read-only GUI available from a clean checkout on another computer.

Validation

• python -m unittest discover -s tests -v — 83 tests passed
• ruff check relay tests — passed
• python build_release.py — passed
• python relay.pyz version — passed (0.6.0)
• GUI smoke tests passed with QT_QPA_PLATFORM=offscreen

Next step

After review/merge and the G0/G1 release bookkeeping, continue with G2: Job control and New Task.