fix(proactive): PROACTIVE=false means no suggestions, including 'want me to run /X?' (W5.1)

The router forbade suggesting skills when PROACTIVE is false while the preamble
told the model to ask 'want me to run it?'. Decision: false means never
auto-invoke and never suggest, including by asking. The preamble line in
generate-upgrade-check.ts now matches the router, and both quote the value
as `false`, the way gstack-skill-start prints it. Restore with
gstack-config set proactive true.

W7a pin: test/gen-skill-docs.test.ts:4488 used the old quoted sentence as a
preamble-order marker; it now finds the PROACTIVE-false rule with a
quote-tolerant, case-insensitive pattern.

test/gen-skill-docs.test.ts

@@ -4485,7 +4485,7 @@ describe('plan-mode-info resolver (handshake-replacement)', () => {
       'utf-8',
     );
     const planModeIdx = content.indexOf(PLAN_MODE_INFO_MARKER);
-    const upgradeIdx = content.indexOf('If `PROACTIVE` is `"false"`');
+    const upgradeIdx = content.search(/If `PROACTIVE` is `"?false"?`/i);
     expect(planModeIdx).toBeGreaterThan(0);
     expect(upgradeIdx).toBeGreaterThan(0);
     expect(planModeIdx).toBeLessThan(upgradeIdx);