chore(build): untrack generated frontend dist

[blak0p]

Closes #82

Summary

• Stops versioning Vite-generated frontend output under cmd/x6configurator/frontend/dist/**.
• Generates frontend assets before Go and Wails build/test paths.
• Aligns contributor, build, OpenSpec, and Wails guidance with the clean-checkout workflow.

Changes

File	Change
.gitignore	Ignores generated frontend dist output.
Makefile	Generates frontend assets before Go/Wails operations.
README.md, CONTRIBUTING.md, docs/config/guidance	Documents the generation-first build policy.
cmd/x6configurator/frontend/dist/**	Removes the three tracked generated files.

Test Plan

• (cd frontend && npm ci && npm run build)
• go build ./...
• go test ./...
• go test ./cmd/x6configurator
• go vet ./...
• (cd frontend && npm test)
• Makefile dry-run ordering and ignored/index checks
• make check final Wails build — locally blocked because wails3 is unavailable; CI/release provisions it.

Delivery note

Native reliability review approved this candidate. It reported one non-blocking follow-up about parallel Make targets sharing frontend generation.