refactor(project): load icons from .opencode assets

[anduimagui]

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

The new resolution behavior prioritizes icon files inside .opencode/icon/ first, then falls back to .opencode/**/favicon.*, and then keeps discovery fallback for repository favicon files. It also adds support for .url files (direct URL/data URL or URL=... format).

How did you verify your code works?

• Updated tests in packages/opencode/test/project/project.test.ts for .opencode icon priority behavior.
• Removed config-schema tests that validated icon in opencode.json.
• Ran:
  • bun test test/project/project.test.ts test/config/config.test.ts (from packages/opencode)
• In this environment, test execution is currently blocked by local git hook/tooling behavior in temp repos (lefthook/mint command failures), so full local verification is incomplete.

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Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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