chore: migrate from husky to native git 2.54 config-based hooks

[jevonearth]

Summary

Replaces husky with Git's built-in config-based hooks (Git 2.54+, release notes). The single pre-commit hook (npm run precommit) now lives in a tracked .githooks.config, wired into .git/config via include.path by a prepare script.

• Removes husky devDependency (net -1 package; husky 9 has zero transitives).
• No more .husky/_/husky.sh shell-sourcing dance.
• Hook commands stay tracked and reviewable in the repo.

Behavior details

Old Git handling. scripts/setup-hooks.sh warns to stderr and exits 0 on Git < 2.54 instead of failing. Needed because ubuntu-latest currently ships Git 2.53, so npm ci would otherwise fail in CI before build/test. Contributors on old Git see a loud message explaining why hooks won't run.

core.hooksPath safety. Only unset when it equals .husky/_ (the old husky pointer). Any other value — including a contributor's intentional custom hook directory — is left alone.

Idempotent. Repeat npm install runs don't duplicate the include.path entry.

Tarball/CI-without-.git safety. If there's no .git directory, the script exits 0 cleanly.

Verify

git --version              # need >= 2.54 for hooks to run
npm install                # prepare script wires things up
git hook list pre-commit   # should show "precommit"

Disable locally without editing the config:

git config --local hook.precommit.enabled false

Test plan

• Fresh clone + npm install wires include.path; git hook list pre-commit shows precommit
• Committing runs the full workspace precommit (lint-staged fanout), blocks on failure
• Second npm install run does not duplicate include.path
• With core.hooksPath=.husky/_, script unsets it
• With core.hooksPath=/some/user/path, script leaves it alone
• No .git present → script exits 0
• CI green on ubuntu-latest (Git 2.53) — prepare should warn + exit 0, not fail

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.03%. Comparing base (22cabdc) to head (23c646b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3415   +/-   ##
=======================================
  Coverage   80.03%   80.03%           
=======================================
  Files         250      250           
  Lines       14928    14928           
  Branches     3682     3682           
=======================================
  Hits        11948    11948           
  Misses       2980     2980           

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