feat(network): add fetch timeouts to GitHub API and Git operations

[gregpriday]

Summary

• Adds explicit timeouts to all GitHub GraphQL/REST calls and simple-git operations so the app no longer hangs during API outages or slow networks
• GitHub GraphQL gets a 15s per-request timeout via AbortController signal, REST fetch calls get the same treatment
• simple-git operations get a 30s timeout for local commands and 30s for network commands via the timeout constructor option
• Timeout errors flow through the existing parseGitHubError handler and cache fallback, so timed-out requests serve stale data instead of freezing the UI

Resolves #3697

Changes

• electron/services/github/GitHubAuth.ts — createClient() now accepts an optional AbortSignal and wires it into the Octokit request options
• electron/services/GitHubService.ts — All GraphQL calls create an AbortController with 15s timeout; REST fetch uses AbortSignal.timeout()
• electron/services/GitService.ts — simpleGit() constructor receives timeout config
• electron/utils/git.ts — createGit() utility updated with timeout parameter
• electron/workspace-host/WorkspaceService.ts and WorktreeMonitor.ts — git instances created with timeouts
• Various IPC handlers and services updated to pass timeout config through createGit()

Testing

• Added unit tests for GitHubAuth timeout error handling
• Updated existing git utility tests for the new timeout parameter
• Updated workspace service test mocks for createGit signature change
• npm run check passes clean (typecheck + lint + format)

[gregpriday]

Review status: Rebased and ready

• Merge sequence: merge after PR feat(security): harden simple-git against malicious repo config RCE #3742 (hardened git)
• Semantic conflict with PR feat(security): harden simple-git against malicious repo config RCE #3742: Both PRs replace simpleGit() calls across the codebase. feat(security): harden simple-git against malicious repo config RCE #3742 introduces createHardenedGit() with security config overrides; this PR introduces createGit() with block timeouts. After feat(security): harden simple-git against malicious repo config RCE #3742 merges, this PR will have conflicts in git-write.ts, projectCrud.ts, GitService.ts, git.ts, and more. Resolution: add the timeout option into createHardenedGit() from feat(security): harden simple-git against malicious repo config RCE #3742, then use createHardenedGit everywhere (drop createGit).