feat(reliability): Outbox Poller Hangfire job with inbox idempotency

Implement async outbox polling and event publishing to inbox using Hangfire.
Completes AGENTS.md v16.0 Outbox/Inbox crash-recovery validation gate.

Changes:
- DapperOutboxMessageReader: async reader with InsertInboxAsync for idempotent publishing
- OutboxPollerJob: recurring Hangfire job (q-research, 3 retries, max 100 batch)
  * Polls unpublished messages (PIT-safe cutoff: now - 5 min)
  * Publishes to inbox_message (consumer='outbox-poller')
  * Marks published_at + increments attempt counter
  * Dead-letters messages after 3 attempts
- Program.cs: Register DapperOutboxMessageReader, schedule outbox-poller every minute UTC
- appsettings.json: Kestrel 5002 port binding for nginx upstream
- Integration.Tests: 3/3 passing scenarios (normal, PIT cutoff, max-attempts)

AGENTS.md v16.0 Checklist:
✅ SOLID (single responsibility, DI)
✅ Complexity (cyclomatic < 10)
✅ Audit (PIT query, published_at tracking, attempt counter)
✅ Necessity (CLAUDE.md: "Hangfire job polls outbox, publishes events")
✅ Normalization (3NF outbox, idempotent inbox PK, job_run audit)
✅ Simplicity (schema-qualified SQL, no SELECT *)
✅ Pattern (Hangfire job, on conflict do nothing)
✅ Guardrails (no magic values, crash-safe)
✅ Traceability (EventIds, LoggerMessage, correlation_id)
✅ Safety (atomic operations, idempotent inbox, no partial success)
✅ Maturity (Contract→Implementation→Test: 3/3 passing)
✅ Right Way (no force/no-verify, proper retry classification)
✅ Debt (zero new tech debt; consumer='outbox-poller' minimal & extensible)

Validation gates: 5/8 passed
- ✅ .NET 10 build/test
- ✅ pnpm typecheck/build
- ✅ DbUp fresh/upgrade
- ✅ Kestrel 5002 + nginx verified
- ✅ Outbox/Inbox crash-recovery

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/KArtSell.Host/appsettings.json

@@ -1,4 +1,11 @@
 {
+  "Kestrel": {
+    "Endpoints": {
+      "Http": {
+        "Url": "http://127.0.0.1:5002"
+      }
+    }
+  },
   "ConnectionStrings": {
     "Postgres": "Host=localhost;Port=5432;Database=kartsell;Username=kartsell;Password=kartsell"
   },