feat(tier2): smarter fraud detection — Block G

Per-event fraud tuning. Hosts can now dial the medium / high / block
boundaries, allowlist trusted networks, and feed verdicts back on
flagged accesses — the seed corpus for a future ML model.

Schema (migration 0011)
- events.fraud_{medium,high,block}_threshold default 30/60/85 so
  existing events behave identically until a host changes them
- access_logs.geo_{country,city,lat,lon} for future enrichment
- fraud_feedback table — verdict ('legitimate' | 'suspicious') + note,
  PK on access_log_id so re-mark is an upsert
- event_allowlists table — (event_id, ip_cidr) primary key, inet column
  so containment checks use the native >>= operator (indexed lookup)

Domain
- FraudThresholds with Valid() + Band() helpers; Default trio echoed
  through GET responses so the frontend doesn't duplicate constants
- ParseAllowlistCIDR accepts bare IPs (auto-widens to /32 or /128) and
  canonicalises the output (203.0.113.42 → 203.0.113.42/32)
- Event.Thresholds() falls back to defaults if columns weren't
  populated yet, so the API never wedges every score into "low"

Storage
- AllowlistRepo: List / Add / Remove + Matches() — the latter pushes
  CIDR containment into Postgres rather than streaming rows back
- FeedbackRepo: Record (upserts) + ListForEvent (joined through guests)
- EventRepo.GetThresholds + UpdateThresholds, plus the threshold
  columns baked into scanEvent so every event load carries them
- AccessLogRepo.BelongsToEvent — stops a hostile editor on event A
  from marking event B's access logs

API
- GET/PUT /events/{id}/security/thresholds (viewer/editor)
- GET/POST/DELETE /events/{id}/security/allowlist
- POST /events/{id}/access-logs/{log_id}/feedback (editor)
- GET /events/{id}/security/feedback
- RSVP scoring path: allowlist short-circuit fires before the fraud
  engine; the engine's score is then re-banded against the event's
  thresholds (engine.Risk becomes advisory — API is the source of
  truth for "what counts as block here")
- CORS Allow-Methods already includes PUT (Block D fix)

Fraud engine
- Single-signal cap: it now takes ≥2 sub-scores of ≥70 to push the
  final into HIGH. Fixes the well-known "second visit with a slightly
  shifted fingerprint scores 60+" false positive
- Engine band remains advisory; API re-bands using per-event
  thresholds before deciding to block

Frontend
- SecurityCard.vue: visual band ribbon (proportional to thresholds),
  three sliders with mutual clamping so dragging medium past high
  pushes high (not an invalid ordering), reset-to-defaults button,
  CIDR allowlist with inline add + per-row remove, verdict-history
  inbox. Toast feedback on save/add/remove
- "Security" tab added to the event-detail tab nav (5th tab,
  right of Analytics)
- Viewer role hides write affordances; server enforces too

Tests
- Domain: ThresholdsBand, ThresholdsValid, ParseAllowlistCIDR (bare
  IP widening + traversal/typo rejection), FraudFeedbackValid
- Integration: thresholds round-trip + invalid ordering rejection,
  allowlist CRUD + duplicate 409 + invalid CIDR 400 + IP auto-widen,
  feedback record + upsert + cross-tenant 404 + invalid verdict 400,
  viewer can read / editor can write / outsider gets 404
- Full integration suite green (315.8s, all 36 top-level tests pass)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/nuxt.config.ts

@@ -12,6 +12,25 @@ export default defineNuxtConfig({
         { name: 'viewport', content: 'width=device-width, initial-scale=1' },
         { name: 'description', content: 'Real-time fraud detection for event RSVPs.' },
       ],
+      // Tier 2 Block D — preload the curated branding-font allowlist so
+      // the host's font picker actually changes how the RSVP page looks.
+      // Without these, every choice silently falls back to the system
+      // default font. preconnect cuts ~150ms off the first paint.
+      link: [
+        { rel: 'preconnect', href: 'https://fonts.googleapis.com' },
+        { rel: 'preconnect', href: 'https://fonts.gstatic.com', crossorigin: '' },
+        {
+          rel: 'stylesheet',
+          href:
+            'https://fonts.googleapis.com/css2' +
+            '?family=Playfair+Display:wght@400;600;700' +
+            '&family=Cormorant+Garamond:wght@400;500;600' +
+            '&family=Lora:wght@400;500;600' +
+            '&family=DM+Sans:wght@400;500;600' +
+            '&family=Manrope:wght@400;500;600' +
+            '&display=swap',
+        },
+      ],
     },
   },
   runtimeConfig: {