feat(desktop): open existing sessions from deep links

[filantus]

Issue for this PR

Closes #44167

Type of change

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

What does this PR do?

Adds opencode://open-session?server=...&session=... links for existing Desktop sessions. The app resolves the configured server plus canonical session lineage before navigating.

Adds Copy link to the custom session-tab context menu introduced by #46116. It copies the public URL on Desktop and an absolute web URL in the browser, with localized success/error feedback.

Desktop forwards protocol URLs from both initial startup arguments and second-instance delivery. Deep-link handling is serialized so launches are processed in delivery order, while a single argument batch uses its last supported URL.

This complements #44137: that PR creates a new session from an external URL, while this one opens an existing Desktop session.

How did you verify your code works?

• bun test --conditions=solid --preload ./happydom.ts ./src/pages/layout/helpers.test.ts from packages/app (33 passed)
• bun test ./src/main/deep-links.test.ts from packages/desktop (2 passed)
• bun run typecheck from packages/app and packages/desktop (passed)
• bun turbo typecheck via the pre-push hook after merging upstream dev (30 tasks passed)
• Prettier check passed; targeted oxlint reported no errors, with five warnings on unchanged lines
• Original deep-link routing was manually tested in an unpacked Windows build. The restored Copy link menu was manually tested in a separate local Desktop build.

Screenshots / recordings

The session-tab context menu now contains Rename, Copy link, and Close tab. No screenshot is attached.

Checklist

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

[dekart]

I'd love to see this feature added