feat(gen): strip gen-time-only frontmatter keys from Claude renders

interactive + benefits-from are read from the .tmpl by buildContext at
generation time; no runtime, host, or test reader consumes them from the
generated SKILL.md (e2e-harness-audit reads .tmpl; benefits-from tests
assert rendered prose). gbrain: stays (bin/gstack-brain-context-load reads
it from the installed render); hooks: stays (Claude Code host wires
PreToolUse from it).

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

hosts/claude.ts

@@ -8,7 +8,14 @@ const claude = defineHost({
 
   frontmatter: {
     mode: 'denylist',
-    stripFields: ['sensitive', 'voice-triggers'],
+    // interactive + benefits-from are gen-time inputs (buildContext reads them
+    // from the .tmpl); no runtime or test reader consumes them from the
+    // GENERATED file (verified: e2e-harness-audit reads .tmpl; benefits-from
+    // tests assert rendered prose; the host reads name/description/
+    // allowed-tools/hooks; bin/gstack-brain-context-load reads gbrain: — which
+    // is why gbrain and hooks are NOT stripped). Stripping them trims the
+    // always-on frontmatter catalog every session loads.
+    stripFields: ['sensitive', 'voice-triggers', 'interactive', 'benefits-from'],
     descriptionLimit: null,
   },