chore(tooling): add a pre-commit hook for the fast committing gates

CLAUDE.md's five-command "Before Committing" list was enforced by memory
alone. scripts/hooks/pre-commit now runs the half of it that finishes in
seconds — `bun run check`, `bun run test`, check-frontend-boundary.sh, and
`cargo fmt --all -- --check` only when staged files touch src-tauri/.

`cargo clippy` and `cargo test` are left out on purpose. Minutes per commit is
how a hook teaches people to type --no-verify; CI and `bun run test:all` are
where the slow gates belong.

Installed via `bun run hooks:install`, which sets core.hooksPath to the
tracked scripts/hooks directory rather than copying into .git/hooks, so later
changes to the hook reach everyone on their next pull.

The hook runs every gate before reporting, so one commit tells you everything
that is wrong rather than only the first thing. It exits 0 without running
anything during a merge, rebase, or cherry-pick, and when nothing is staged;
`git commit --no-verify` skips it as usual.

scripts/install-hooks.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# Point git at the repo's tracked hooks directory.
+#
+# TRACES: | DR-207
+#
+#   bun run hooks:install        # or: ./scripts/install-hooks.sh
+#
+# `core.hooksPath` is used rather than copying files into .git/hooks so the
+# hooks stay version-controlled: an update to scripts/hooks/pre-commit reaches
+# everyone on their next pull instead of needing a re-install.
+#
+# The setting is local to this clone (git config, not committed). To undo:
+#   git config --unset core.hooksPath
+
+set -euo pipefail
+
+REPO_ROOT="$(git rev-parse --show-toplevel)"
+cd "$REPO_ROOT"
+
+HOOKS_DIR="scripts/hooks"
+
+if [ ! -d "$HOOKS_DIR" ]; then
+  echo "❌ $HOOKS_DIR does not exist — are you in the JellyTau repo?" >&2
+  exit 1
+fi
+
+# Git refuses to run a hook that is not executable, and the bit is easy to lose
+# on a fresh checkout on some filesystems.
+chmod +x "$HOOKS_DIR"/* 2>/dev/null || true
+
+git config core.hooksPath "$HOOKS_DIR"
+
+echo "✅ core.hooksPath = $(git config core.hooksPath)"
+echo ""
+echo "Installed hooks:"
+for hook in "$HOOKS_DIR"/*; do
+  [ -f "$hook" ] || continue
+  echo "  - $(basename "$hook")"
+done
+echo ""
+echo "pre-commit runs: bun run check, bun run test, check-frontend-boundary.sh,"
+echo "and cargo fmt --check when src-tauri/ is staged."
+echo "Bypass a single commit with: git commit --no-verify"