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>

config.yaml

@@ -51,6 +51,14 @@ reddit:
   maxReadyCandidates: 25  # Pause screening when this many posts are ready to send
   # sellerKeywords: [...]  # Uncomment to override default keyword list
 
+conversations:
+  offPlatformKill: true      # End the conversation when they push Telegram/Snapchat/payment/etc.
+  killOnSellerKeyword: true  # Set false to hand seller-keyword hits to an operator instead
+  aiReplyScreening:
+    enabled: false           # Second-stage classifier on inbound replies; fails open
+    killConfidence: 0.8
+    flagConfidence: 0.6
+
 openrouter:
   imageAnalysisModel: "google/gemini-2.5-flash-lite"
   imageAnalysisFallbackModels: