[web] Add Symphony favicon

[sharmila-oai]

Context

Symphony Observability currently uses the browser's generic fallback icon, which makes its control-plane tabs hard to identify.

TL;DR

Add a custom, cache-busted favicon to the Symphony Observability dashboard.

Summary

• Add a generated 128x128 transparent PNG mark for Symphony.
• Serve the favicon through the existing embedded static-asset controller.
• Add a content digest to the favicon URL to avoid stale browser caches.
• Verify the favicon markup, route response, content type, and binary body.

Alternatives

• Keep the generic browser icon. This leaves Symphony tabs difficult to distinguish.
• Embed a data URI in the layout. A normal asset route is easier to cache, test, and replace.

Test Plan

• make -C elixir all
• mix test test/symphony_elixir/extensions_test.exs
• Browser preview at http://127.0.0.1:4022/

[sharmila-oai]

@codex review

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[sharmila-oai]

Replaced the original abstract mark with the selected top-down orchestra seating map: discrete section blocks around a conductor, podium, and baton. The asset was tightly cropped, converted to transparent PNG, and verified at 128px and 32px.

@codex review

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[sharmila-oai]

All required checks are green and the final orchestra seating favicon revision is ready.

@codex review

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[sharmila-oai]

Current-commit review completed for ead0ad3b1ae602ff1497cdd3c3d300caf163ed9a: no actionable findings. The diff follows the existing embedded static-asset pattern, tests the markup and binary response, and contains no private URLs, internal project names, credentials, or local paths. Local make all passed with 241 tests and 100% coverage, and all GitHub checks are green. The automated Codex connector did not respond to three review requests.

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