feat(app) project icon handling

[anduimagui]

Issue for this PR

Refs #13843

Type of change

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

What does this PR do?

This branch expands the original project icon work into a broader cleanup across the backend and app layers.

On the backend, it updates project icon discovery and precedence so .opencode assets are resolved more consistently, including support for .url sources and clearer fallback behavior.

On the app side, it makes project-specific icons render consistently in the sidebar, edit project flow, and new session view. It also extracts shared project avatar logic into a dedicated module so icon source resolution, avatar colors, and fallback behavior live in one place.

Because this branch has grown over time, the scope is now wider than the original PR title and description and should be reviewed as a cross-package icon/avatar update rather than a narrowly scoped backend-only change.

How did you verify your code works?

• Ran repo typechecks through the push hook with bun turbo typecheck
• Updated app-side tests for the shared project avatar helpers
• Updated backend project icon tests in packages/opencode
• Manually verified the new session view now uses the current project icon override instead of the default OpenCode mark

Screenshots / recordings

n/a

Checklist

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

If you do not follow this template your PR will be automatically rejected.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[github-actions]

Hey! Your PR title refactor project icon handling — align discovery, app rendering, and shared avatar helpers doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[hab33bi]

For whatever reason, the icon saving system is broken for me, I try to set a png (high quality as the icon) and it does not save. Windows 11. Latest OpenCode. Reopen this.