ci(hooks): pre-commit security check (mirror of fai/platform)

Mirrors the hook + script from `fai/platform`@1ebf893 verbatim
so commits to fai_studio go through the same gate: secrets,
forbidden filenames, confidentiality references, marketing-
speak, DCO sign-off, Conventional Commits subject, no Claude
co-author trailer.

A `.security-allow` file at the repo root extends the script's
universal excludes with three Studio-specific paths whose
content legitimately includes the filtered terms — the
Today-Hero proposal pipeline (LLM prompt + accept gate), its
runtime loader equivalent, and its operator-facing policy doc.

No CI mirror yet — Studio doesn't have a Forgejo workflow
(Flutter-on-DinD is a chunk of work). The local hook is the
gate for now; CI mirror follows when Flutter CI lands.

Activate once with `bash tools/install-hooks.sh`.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

.githooks/pre-commit

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+# F∆I Platform — pre-commit hook.
+# Activated via `tools/install-hooks.sh` (sets core.hooksPath=.githooks).
+# Scans staged files for secrets, banned phrases, forbidden filenames.
+# Same script runs in Forgejo CI — see .forgejo/workflows/ci.yml.
+exec "$(git rev-parse --show-toplevel)/tools/security/check-staged.sh" content