hooks: refuse master, cap a code commit at 300 lines, require the task ref (V-445)

Two git hooks, tracked in .githooks and wired with core.hooksPath so a
fresh clone gets them with one config line.

pre-commit refuses master and refuses more than 300 changed lines in
non-markdown files. Markdown is exempt because docs land as one batch.
This is a commit-time guard, which diff-budget.sh is not: that hook
blocks the agent's edits and says nothing when either of us commits.

commit-msg requires (V-<id>), not (#<id>). Gitea autolinks # to its own
issues, and Vikunja is the tracker.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.githooks/commit-msg

@@ -0,0 +1,30 @@
+#!/bin/sh
+# Every commit names the Vikunja task it belongs to.
+#
+#   router: narrow the single-token rule (V-359)
+#
+# V- and not #, because Gitea autolinks #359 to a Gitea issue, which is a
+# different tracker and a wrong link.
+#
+# Exempt: merges, reverts, fixup/squash, and the initial commit.
+
+msg_file=$1
+subject=$(sed -n '1p' "$msg_file")
+
+case "$subject" in
+	Merge\ *|Revert\ *|fixup!\ *|squash!\ *|amend!\ *) exit 0 ;;
+esac
+
+if [ -f "$(git rev-parse --git-dir)/MERGE_HEAD" ]; then
+	exit 0
+fi
+
+if printf '%s' "$subject" | grep -qE '\(V-[0-9]+\)$'; then
+	exit 0
+fi
+
+echo "commit-msg: subject must end with a Vikunja task ref." >&2
+echo "  got:  $subject" >&2
+echo "  want: router: narrow the single-token rule (V-359)" >&2
+echo "  No task yet? Create one. Work without a task is work nobody can resume." >&2
+exit 1