Fix frontend validation readiness in worktrees

[adriandemian]

Summary

• Tighten frontend validation handling in worktrees so validation discovers the frontend/ package context, runs from the package directory, and uses the local Vitest binary rather than a root/global fallback.
• Add backend readiness checks around frontend install/validate steps so partial node_modules trees do not count as ready just because the directory exists.
• Expand merge-validation coverage for frontend readiness edge cases, including command sanitization, cached success paths, package.json-based frontend detection, and readiness failure handling.
• Include a small metrics IPC contract adjustment so workspace delivery-trend counts stay aligned with the current event-backed model.

User Impact

Frontend worktrees should now validate against the actual app package instead of accidentally treating the repository root as the execution context. That reduces false-ready installs, avoids running the wrong Vitest binary, and makes readiness failures surface before validation proceeds.

The metrics IPC change keeps workspace-count reporting consistent with the delivery-trend contract used by the UI and tests.

Technical Context

• agents/ralphx-project-analyzer/shared/prompt.md now tells the analyzer to emit path: "frontend" when the only Node package lives under frontend/package.json, and it avoids passing vitest.config.ts as a test target.
• A new frontend_readiness module centralizes frontend-specific cwd selection, Vitest command sanitization, package-context detection, executable checks, and Node import probes for vitest/config, react, zod, and @tauri-apps/api.
• run_install_phase and run_validate_phase now consult that readiness logic before skipping installs or starting validation, and they fail early when frontend dependencies are still incomplete.
• Merge-validation state now carries an optional install command on analysis entries so validate can bootstrap missing frontend dependencies before retrying validation.
• The merge-validation test suite adds focused regression coverage for the new frontend readiness behavior and the sanitized Vitest command paths.
• src-tauri/tests/metrics_commands.rs was updated to keep the IPC delivery-trend contract aligned with the workspace-count expectations.

Risks / Follow-Ups

• Frontend validation is now stricter about what counts as ready, so any incomplete or unusual local package layout may fail earlier than before.
• The readiness checks rely on package inspection and import probes; if a project uses an atypical frontend stack, it may need an explicit validation shape that fits this detection.
• Vitest command sanitization is targeted at the command forms covered here, so other custom invocation patterns may still need follow-up if they appear in real projects.

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Generated by RalphX

[codecov]

Codecov Report

❌ Patch coverage is 89.82456% with 29 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ne/transition_handler/merge_validation/validate.rs	84.84%	15 Missing ⚠️
...ion_handler/merge_validation/frontend_readiness.rs	91.77%	13 Missing ⚠️
...ine/transition_handler/merge_validation/install.rs	96.42%	1 Missing ⚠️

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