feat: support configuring default server URL for desktop

[athal7]

Summary

• Allow desktop app to connect to an existing server instead of spawning its own sidecar
• Add UI in server selection dialog to set/clear the default server
• Show connection failure dialog with Retry/Start Local options when configured server is unreachable

Fixes #7371

[github-actions[bot]]

The following comment was made by an LLM, it may be inaccurate:

Based on the search results, I found one potentially related PR:

Related PR:

• #6947: fix(desktop): make dev server port configuration more flexible

This PR is related because it also deals with desktop server configuration, though it focuses on port flexibility rather than the default server URL feature. It may be worth reviewing to understand the existing server configuration approach.

The current PR (#7363) appears to be addressing a distinct feature: allowing the desktop app to connect to a pre-existing server instead of spawning its own sidecar, with UI for managing this connection preference.

[github-actions[bot]]

Hey! Your PR title feat(desktop): support configuring default server URL doesn't follow conventional commit format.

Please update it to start with one of:

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

See CONTRIBUTING.md for details.

[github-actions[bot]]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[adamdotdevin]

@athal7 screenshots please!

[athal7]

https://github.com/user-attachments/assets/111ba57c-70a8-4e52-8deb-0327e2b2666d

[adamdotdevin]

@Brendonovich you good with the tauri side of this one?