feat(wire): integrate errhint, testrunner, installtxn into hawk

[Patel230]

Summary

Wires the Zero-adopted mechanisms (from PR #250) into hawk's running system:

errhint -> error surfacing

• cmd/error_classify.go: friendlyErrorMessage now appends errhint.TUIHint(err) — every TUI error row gets a one-line fixable next step for provider errors. Conservative: local errors draw no hint.
• cmd/exec.go: the headless error event now prints errhint.CLIHint for text output (slash commands don't apply headless).

testrunner -> verify loop

• cmd/verify_cmd.go: hawk verify now discovers project test/verify commands via testrunner.Detect, runs them, and prints structured summaries (passed/total + failure file/message) via testrunner.ParseSummary. Purely additive — existing security-log and governance checks untouched.

installtxn -> skill install

• internal/plugin/registry.go: skill SKILL.md manifest now published via installtxn.WriteFileAtomically (atomic rename, no partial write).

lockutil: no clean fit — hawk's lock sites use kernel flock (session autosave), not O_EXCL files, so it stays a ready primitive rather than a forced fit.

Verification

• New tests: TestFriendlyErrorMessageAppendsProviderHint / NoHintForLocalError, TestRunWorkspaceChecksDetectsGoProject / EmptyDir
• go build ./..., go vet, full cmd/plugin/errhint/testrunner/installtxn/lockutil/minify/tool suites green
• Boundary guard + govulncheck + full pre-push test suite green