Add Gitea-to-Claude-Code-Routines webhook proxy

Express service that authenticates Gitea deliveries, verifies the HMAC
signature, builds a readable text summary for push/pull_request events,
and forwards it to the Anthropic routines API with the headers Gitea
can't set itself. Includes in-memory delivery dedup, structured logging,
.env.example, and a Dockerfile for deployment behind nginx.

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

.env.example

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+# Puerto en el que escucha el proxy (nginx hará proxy_pass hacia aquí)
+PORT=3000
+
+# Valor exacto que Gitea debe enviar en el header "Authorization".
+# Configúralo igual en Gitea (Settings -> Webhooks -> Authorization header).
+GITEA_AUTH_HEADER=changeme-secreto-A
+
+# Secret configurado en el webhook de Gitea, usado para verificar la firma
+# HMAC-SHA256 del header "X-Gitea-Signature".
+GITEA_WEBHOOK_SECRET=changeme-secreto-gitea
+
+# ID de la rutina de Claude Code (parte de la URL /routines/{ROUTINE_ID}/fire)
+ROUTINE_ID=trig_xxxxxxxxxxxxxxxxxxxxxxxx
+
+# Token de la rutina (sk-ant-oat01-...), se envía como "Authorization: Bearer <token>"
+ROUTINE_TOKEN=sk-ant-oat01-changeme
+
+# TTL en milisegundos para el dedup en memoria de entregas de Gitea (X-Gitea-Delivery)
+DEDUP_TTL_MS=300000