[codex] Add pricing alias registry

[raychrisgdp]

Summary

Adds a maintainable pricing alias registry so local model IDs can resolve to canonical OpenRouter pricing IDs instead of silently showing unpriced costs.

What changed

• Centralized pricing alias resolution in dashboard/pricing.py.
• Added target aliases for Codex Spark and observed Antigravity Gemini model IDs.
• Preserved explicit unpriced status for free-suffixed models without a registered alias.
• Added pricing_url metadata for API-equivalent pricing references.
• Linked priced Model Breakdown cost values to their OpenRouter model reference pages.
• Added Hermes model reference URLs for session-accounted costs when the model ID can be resolved.
• Expanded tests for alias resolution, URL exposure, and UI link rendering.

Review focus

• Confirm the alias decisions, especially google/antigravity-gemini-3.1-pro* -> google/gemini-3.1-pro-preview.
• Confirm that OpenRouter model pages are the right URL references for priced cost cells.
• Confirm unpriced/free-suffixed rows remain honestly unpriced rather than guessed.

Validation

• uv sync
• uv run python -m unittest tests.test_app tests.test_readme -v
• uv run python -m py_compile app.py scripts/snapshot_dashboard.py
• scripts/review.sh
• Rendered the local dashboard at http://127.0.0.1:8336/ and verified priced rows have cost links; the DOM check returned pricedWithoutHref: [].