fix: expand ~ and relative paths in Add Repository

[vc1492a]

Description

Fixes Add Repository so typed ~/… and relative paths resolve before detect-branch, project create, and RunPane repo validation. Also stops projects:detect-branch from reporting a fake main when detection fails (UI now shows a failure state).

Closes #577

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have read the CONTRIBUTING.md guidelines
• My code follows the code style of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (N/A beyond in-app tooltip update in AddProjectDialog — no markdown/docs pages referenced the absolute-only wording)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes (see QA notes: issue-specific + frontend green; full main suite has 4 unrelated skillCacheManager failures)
• I have run pnpm typecheck and pnpm lint locally (Node 22.18.0)
• I have tested the Electron app locally with pnpm electron-dev (needs human GUI probes below)

Critical Areas Modified

• Session output handling (requires explicit permission)
• Timestamp handling
• State management/IPC events (touched projects:create / projects:detect-branch and RunPane repo-path validation to expand paths; no session-output changes)
• Diff viewer CSS

Additional Notes

Behavior choices reviewers should know:

• Relative paths resolve against $HOME, not Electron/process cwd (avoids creating repos under / or the app directory).
• Existing paths are realpath’d when present (e.g. /tmp → /private/tmp on macOS), so stored paths become canonical.
• WSL UNC paths (\\wsl.localhost\…, \\wsl$\…) are left unchanged so parseWSLPath still works.
• Create remains allowed when branch detection fails (pre-existing product behavior); only the fake-main lie is removed.
• Remote session dialog’s local main fallback is intentionally untouched.

Manual probes (still need a human in pnpm electron-dev):

• Type ~/path/to/real-repo → Detected Branch matches git branch --show-current; create stores the realpath.
• Bogus path → no Detected Branch main.
• Browse-picked absolute path still works.
• runpane repos add --path '~/…' after this build.

Automated QA (2026-09-03, head 91d13835, Node 22.18.0)

Check	Result
pnpm typecheck	pass
pnpm lint	pass (Node 22.18 required for oxlint TS plugin)
Issue-specific Vitest (pathResolver + detectProjectBranch)	13/13 pass
CI=1 pnpm --filter frontend test	327/327 pass
pnpm rebuild better-sqlite3-multiple-ciphers + CI=1 pnpm --filter main exec vitest run	902 pass / 4 fail / 2 skip — failures only in skillCacheManager.test.ts (Pane Chat guide / idle watcher), unrelated to path expansion
GitHub Actions Code Quality + React Doctor	blocked: action_required (first-time contributor workflow approval)
Socket Security	pass

No review threads yet.

[vc1492a]

Status update from contributor automation

Local verification on head 91d13835 (Node 22.18.0):

• pnpm typecheck ✅
• pnpm lint ✅
• Issue-specific tests ✅ 13/13
• Frontend unit tests ✅ 327/327
• Full main Vitest: 902 passed; 4 failures in skillCacheManager.test.ts only (unrelated to this path-expansion change)

Needs a maintainer (cannot do from this fork account):

1. Approve / enable the pending GitHub Actions workflows for this first-time contributor PR (Code Quality + React Doctor are currently action_required):
   • https://github.com/dcouple/Pane/actions/runs/33710586144
   • https://github.com/dcouple/Pane/actions/runs/33710586304
2. Optional: GUI smoke of Add Repository with ~/… / bogus path / Browse after CI is green (pnpm electron-dev).

Happy to address review feedback once CI can run.