feat(ci): supply-chain hygiene — secret gate on every PR diff, dependency review, OSV, dependabot, evidence-bar PR template

The repo owned a redaction engine and had zero CI-side secret scanning.
quality-gate.yml now pipes every PR diff's ADDED lines through our own
bin/gstack-redact (gate-secret-scan.mjs, taken from the fork — it dogfoods
the engine): HIGH findings fail the check, MEDIUM prints an advisory count
only (no human in CI to confirm), planted-bug fixtures excluded by pathspec.
Live-verified both directions: PEM key fails, clean diff and MEDIUM shapes
pass; ShellCheck (errors) covers the setup/build shell boundary and passes
today; bun audit gates critical advisories. Trigger is pull_request, never
pull_request_target.

dependency-review.yml adopts the hardened never-merged prior-art branch
(fail-on-severity high, workflow paths watched, tight perms) — verify the
dependency graph parses bun.lock with a canary bump before trusting the
gate. dependabot: weekly, grouped per ecosystem, capped PR counts; and
evals.yml image build/push now skips dependabot actors, whose read-only
GITHUB_TOKEN made every lockfile bump a permanently red check. OSV scans
weekly with a reasoned ignore file. All new workflow actions SHA-pinned.
Scorecard deliberately not taken (no consumer for the score).

The PR template front-loads the evidence bar (live proof, liveness
screenshot, no-ETHOS/voice-changes checklist); the unenforced DCO line is
dropped. bin/gstack-verify-gate ships OPT-IN (never registered by ./setup —
a Stop hook running the project's verify command after every turn is the
user's call), with the fork's tests adapted to pin exactly that.

Ported from time-attack/gstack (GStack 2) + our own prior-art branch.

Co-authored-by: Sina Matian <sina@time-attack.dev>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/scripts/gate-secret-scan.mjs

@@ -0,0 +1,31 @@
+#!/usr/bin/env node
+import { spawn } from "node:child_process";
+
+const child = spawn("bun", [
+  "bin/gstack-redact",
+  "--repo-visibility", "public",
+  "--json",
+  "--max-bytes", "16000000",
+], { shell: false, windowsHide: true, stdio: ["pipe", "pipe", "inherit"] });
+let diff = "";
+process.stdin.setEncoding("utf8");
+process.stdin.on("data", (chunk) => { diff += chunk; });
+process.stdin.once("end", () => {
+  const additions = diff
+    .split(/\r?\n/)
+    .filter((line) => line.startsWith("+") && !line.startsWith("+++"))
+    .map((line) => line.slice(1))
+    .join("\n");
+  child.stdin.end(additions);
+});
+let stdout = "";
+child.stdout.setEncoding("utf8");
+child.stdout.on("data", (chunk) => { stdout += chunk; });
+child.once("error", (error) => { throw error; });
+child.once("close", (code) => {
+  const report = JSON.parse(stdout);
+  const high = Number(report.counts?.HIGH ?? 0);
+  const medium = Number(report.counts?.MEDIUM ?? 0);
+  console.log(`credential scan: ${high} high, ${medium} advisory`);
+  process.exitCode = high > 0 || report.oversize || ![0, 2, 3].includes(code) ? 1 : 0;
+});