feat: kill conversations on off-platform and seller pushes

Seller detection on replies was a case-insensitive substring match over the
configured keyword list, and every hit landed in `human-required` alongside
genuine prospects that need a person. Off-platform pushes were only checked
for r4r policy modes, as were the under-18 signals.

Three layers now:

- New `off-platform-signals` module matches on normalized text (unicode
  folding, zero-width stripping, leet mapping, separator removal), so
  `0nlyf4ns`, `t3l3gr4m` and `t e l e g r a m` are caught. Ambiguous terms
  need context: `snap` on its own stays a photo request, never a kill.
- New terminal `killed` automation status. It records the evidence, sets the
  durable seller flag, supersedes the pending claim, and resolves triage to
  `done`, so killed conversations leave every actionable queue. Off-platform
  kills are independent of `reddit.filterSellers`.
- Optional AI screening of inbound replies behind
  `conversations.aiReplyScreening` (off by default). Runs only after the
  deterministic gates pass, memoizes per inbound event, and fails open.

Under-18 and in-person/contact-detail signals now apply to every policy mode
rather than r4r only, and remain human handoffs rather than kills.

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

tests/conversation-triage.test.ts

@@ -90,7 +90,9 @@ describe('conversation triage', () => {
         .toBe('Manual — image received');
       expect(manualFlowLabel(chat({ username: 'c', automationStatus: 'active', automationPolicyMode: 'manual' })))
         .toBe('Manual by policy');
-      expect(manualFlowLabel(chat({ username: 'd', automationStatus: 'active' }))).toBeNull();
+      expect(manualFlowLabel(chat({ username: 'd', automationStatus: 'killed' })))
+        .toBe('Killed — seller');
+      expect(manualFlowLabel(chat({ username: 'e', automationStatus: 'active' }))).toBeNull();
     });
   });