rotate: 4 SaaS-token/app-signing drivers + data-separated proof tracking

Add gitlab, cloudflare, ghactions (MOCK-ONLY) and appsecret (LIVE-VM) one-file
Rotators, each with a table-driven cutover-proof + leak-check test. gitlab/
cloudflare/ghactions are in-place SaaS-token rolls (self/rotate, value-roll,
sealed-secret overwrite) so RevokeOld is a no-op; ghactions seals via
nacl/box.SealAnonymous (no new go.mod dep). appsecret regenerates a local app
signing secret and rewrites it in place across every target file (atomic, mode-
preserving, redacted errors), discoverable via exact-match app-signing key names
in env.go.

Keep real-rotation code distinct from mock code: how each driver's cutover was
validated lives as DATA in internal/rotate/proofs.go (single source of truth) +
docs/ROTATION-PROOFS.md, surfaced as a PROOF column in `incredigo rotate` so a
MOCK-ONLY driver can never be mistaken for a LIVE-VM one. appsecret proven LIVE-VM
against real local files in the sandbox VM.

82 tests green, -race clean on rotate/sink/vault.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/discover/scanners_test.go

@@ -141,6 +141,61 @@ func TestEnvScanner(t *testing.T) {
 		"pgSECRET", "redisSECRET", "weak")
 }
 
+// TestEnvScannerAppSecret proves an app SIGNING secret (SECRET_KEY) is tagged
+// Source="appsecret" with a self-contained blob carrying its value AND file path, so
+// the local in-place rotator can Detect+Rotate it straight from a .env scan — while a
+// generic API key in the same file stays a plain env secret.
+func TestEnvScannerAppSecret(t *testing.T) {
+	dir := t.TempDir()
+	t.Chdir(dir)
+	appVal := "django-insecure-0123456789abcdefghijABCDEF"
+	writeFixture(t, filepath.Join(dir, ".env"),
+		"SECRET_KEY="+appVal+"\nSTRIPE_API_KEY=sk_live_keepGenericEnv00\n")
+
+	v := vault.New()
+	defer v.Purge()
+	creds, err := (&envScanner{}).Scan(context.Background(), v)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var app *Credential
+	for i := range creds {
+		if creds[i].Source == "appsecret" {
+			app = &creds[i]
+		}
+	}
+	if app == nil {
+		t.Fatalf("SECRET_KEY not tagged Source=appsecret; got %+v", creds)
+	}
+	if app.Identity != ".env / SECRET_KEY" {
+		t.Errorf("unexpected identity %q", app.Identity)
+	}
+
+	// The blob must round-trip the value AND the file path for the rotator.
+	buf, _ := v.Open(app.Secret)
+	u, err := url.Parse(strings.TrimSpace(string(buf.Bytes())))
+	if err != nil || u.Scheme != "appsecret" {
+		t.Fatalf("appsecret blob malformed: %v (%q)", err, string(buf.Bytes()))
+	}
+	if u.Query().Get("val") != appVal {
+		t.Error("appsecret blob does not carry the signing value")
+	}
+	if got := u.Query().Get("path"); !strings.HasSuffix(got, ".env") {
+		t.Errorf("appsecret blob path missing/wrong: %q", got)
+	}
+
+	// The generic API key in the same file must NOT be tagged appsecret.
+	for _, c := range creds {
+		if c.Source == "appsecret" && strings.Contains(c.Identity, "STRIPE") {
+			t.Error("generic API key wrongly tagged appsecret")
+		}
+	}
+
+	// Leak-check: the signing value must not appear in any non-secret field.
+	assertNoLeak(t, creds, appVal)
+}
+
 func TestNetrcScanner(t *testing.T) {
 	home := t.TempDir()
 	t.Setenv("HOME", home)