feat(desktop): complete project git workflows

[thomaspblock]

Summary

Projects now supports the complete desktop Git collaboration loop: users can clone repositories, compare pushed branches, open pull requests, publish updates after pushes, request reviews, approve changes, and merge eligible pull requests without leaving Buzz.

• Make pull request creation repository-aware with explicit base and compare branch selection, preserving the selected target branch through merge.
• Add repository-scoped issue creation from project details and the global create menu.
• Support delegated repository ownership for managed agents while restricting approvals, updates, review requests, and merges to trusted identities.
• Validate Git destinations and pull request metadata before native operations; authenticated merge fetches now retain full source history, allow realistic remote timeouts, and publish monotonic merged-status timestamps.
• Prevent duplicate issue, pull request, and reviewer submissions, and avoid local Git queries while creation dialogs are closed.
• Keep the mock Tauri bridge out of production bundles through an explicit E2E build mode.
• Align repository, issue, pull request, commit, and activity views around consistent filters, rounded list containers, metadata columns, and creation controls.

Validation

• Desktop typecheck, Biome checks, structural source checks, and production build
• Focused project pull request unit tests, including trusted approvals and update authorization
• Focused Rust Git workflow tests and desktop Tauri Clippy with warnings denied
• Playwright smoke coverage for pull request creation/review, delegated and rejected merges, duplicate submission guards, commits, issues, and aligned project lists
• Production build verified to contain no E2E bridge chunk
• Full integration setup is blocked locally by pre-existing Postgres migration state (channel_type already exists); this is unrelated to the branch changes

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[thomaspblock]

🤖 ## Updated project screens

Overview

Workspace totals, recent project activity, people, and contribution history.

Repositories

Repository cards with ownership, activity totals, contributors, and language distribution.

Pull Requests

Pull request cards with repository context, status, author, and review actions.

Issues

Issue cards with repository context, age, status, and commit references.

[thomaspblock]

🤖 ## Project detail screens

README

Repository overview with source controls, project metadata, people, and language summary.

Files

Remote repository browser with branch controls and latest commit context.

Commits

Branch commit history with authors, timestamps, hashes, and copy actions.

Issues

Repository-scoped issue list and creation action.

Pull Requests

Repository-scoped pull request list with branches and status.

Contributors

Repository contributors with commit totals and latest activity.