chore(hooks): cut the Zig residue the retirement left behind

Neither hook has dispatched a Zig lint or unit lane since M175 retired the
Zig gating. What survived was residue that reads like live wiring:

- `.githooks/pre-commit` declared `needs_lint_zig=0` and never set or read
  it — not in `any_needed`, not in `make_targets`. Dead since the lane was.
- `.githooks/pre-push` documented `.github/workflows/{test-integration,
  memleak}.yml` as where the heavy lanes moved to, and told the reader that
  `orly gate pr` runs `make memleak` and `make test-integration`. All four
  are deleted. The comment pointed at nothing.

The one live `*.zig` trigger stays: it reaches `check-documentation-rules`,
not a lint lane, because `scripts/check_documentation_rules.py:69` carries
`.zig` in `SCAN_SUFFIXES` and reads command help text out of that source.
The daemon is frozen, not gone — the revision built from it serves api-dev,
so its help text is still user-visible and still worth gating. pre-push now
says so, which is why nobody has to re-derive it next time.

Verified: `bash -n` clean on both · `shellcheck -S error` clean on both ·
`grep -n 'needs_lint_zig' .githooks/*` → no output.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>