feat(tool): port zero minify, errhint, lockutil, installtxn, testrunner

[Patel230]

Summary

Adopts five self-contained, stdlib-only mechanisms from the Zero terminal coding agent (github.com/gitlawb/zero), each verified against hawk, idiomatic, and fully tested.

1. internal/minify — token-cheaper read-only file views. Go minified via the real go/parser AST (guaranteed valid); other languages via a string-aware comment stripper; safe whitespace fallback otherwise. Wired into the Read tool as a minify flag (never changes disk).

2. internal/errhint — classify provider errors (Auth/RateLimit/Connectivity/ModelNotFound/ContextOverflow) into a one-line fixable hint, gated on provider markers so local errors never draw a bogus hint. Careful standalone status-code matching.

3. internal/lockutil — race-correct atomic stale-lock reclaim (rename-aside → liveness probe → live-restore with no-overwrite fallback), POSIX + Windows.

4. internal/installtxn — cross-process staged install/remove with rollback (plugin/skill install paths), POSIX flock + Windows LockFileEx.

5. internal/testrunner — auto-detect test/verify commands (Go/npm/bun/pnpm/yarn/pytest/cargo) and parse runner output into structured counts + failure locations.

All five are boundary-compliant (zero eyrie/client imports; inline/portable, no new external deps beyond golang.org/x/sys already in go.mod). README adopted-capabilities table updated.

Verification

• ~25 new tests across the five packages + minify-in-Read integration
• go build ./..., go vet, full ./internal/{minify,errhint,lockutil,installtxn,testrunner,tool} suites green
• Cross-compile: Windows + darwin builds of the platform-tagged lock/installtxn files OK
• All pre-push boundary guards + govulncheck + full test suite green