chore(ci): tighten CODEOWNERS + drop overclaim in workflow comment

Round-3 PR re-review follow-ups:

LOW — CODEOWNERS missed /scripts/build-plugins-index.mjs and
/wrangler.toml. Both can change the bytes that get signed without
touching the sign step. Replaced the per-file enumeration with /scripts/
catch-all and added wrangler.toml.

HIGH — workflow comment said the post-sign verify step "catches a buggy
or tampered sign-script run". The "tampered" claim was wrong: any
attacker who can edit sign-plugins-index.mjs in a PR can edit the
verify step (and the embedded pubkey) in the same diff. Re-stated as
"catches accidental regressions only — CODEOWNERS is what stops
adversarial edits".

Branch protection on main has been enabled separately via gh API
(force-push + deletion blocked, PR review required, CODEOWNERS
enforced; bypass for repo owner and github-actions[bot] so the
auto-publish workflow keeps working).

.github/CODEOWNERS

@@ -19,11 +19,13 @@
 #   - restrict who can push directly to main (org admins only)
 
 # ---- Signing infrastructure (highest sensitivity) ----
-/scripts/sign-plugins-index.mjs    @suzukaze-haduki
-/scripts/build-plugins-index.mjs   @suzukaze-haduki
-/scripts/build-registry-index.mjs  @suzukaze-haduki
+# Anything that influences the bytes that get signed, OR the signing
+# step itself, requires owner approval. Build-script edits change the
+# bytes that get signed even though they don't touch the sign step.
+/scripts/                          @suzukaze-haduki
 /.github/workflows/                @suzukaze-haduki
 /.github/CODEOWNERS                @suzukaze-haduki
+/wrangler.toml                     @suzukaze-haduki
 
 # ---- Auto-generated artefacts (must not be hand-edited) ----
 /plugins-index.json                @suzukaze-haduki