chore: Dockerfile, Gitea CI image build, docker-compose example

The server now stops on SIGTERM/SIGINT so docker stop is immediate.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker-compose.example.yml

@@ -0,0 +1,26 @@
+# Example: run mangabaka-seeder behind your reverse proxy.
+# Copy to docker-compose.yml, set MBSEED_PUBLIC_URL to the address your proxy serves, then:
+#   docker compose up -d
+# All settings: docs/ARCHITECTURE.md, "Running the server".
+services:
+  mangabaka-seeder:
+    image: gitea.lucaswinther.info/lucasw89/mangabaka-seeder:latest
+    restart: unless-stopped
+    # Only the reverse proxy should reach it; it terminates TLS and appends X-Forwarded-For.
+    ports:
+      - "127.0.0.1:8787:8787"
+    environment:
+      # Public origin (no path). Stored covers are served from it, and the userscript may connect to it.
+      MBSEED_PUBLIC_URL: https://mbseed.example.org
+      # Rehost covers on this server for 30 days. Remove both lines to run without storage
+      # (the page then offers litterbox, catbox and no rehosting).
+      MBSEED_STORAGE_DIR: /data/covers
+      MBSEED_STORAGE_MAX_BYTES: "1073741824" # 1 GiB; uploads past it get 507, nothing is evicted early
+      # Rate-limit on the address your proxy appends to X-Forwarded-For. Leave unset without a proxy.
+      MBSEED_TRUST_PROXY: "1"
+    volumes:
+      # A named volume works as is. For a bind mount, make the directory writable by uid 1000 (the image's "bun" user).
+      - covers:/data/covers
+
+volumes:
+  covers: