feat: support reverse proxy path prefix deployments (#257)

* feat: support reverse proxy path prefixes

* fix: respect BASE_URL in SAML callback fallback

* fix: make BASE_URL runtime configurable

docker-compose.alt.yml

@@ -22,6 +22,7 @@ services:
       #   BETTER_AUTH_URL=https://gitea-mirror.example.com
       #   PUBLIC_BETTER_AUTH_URL=https://gitea-mirror.example.com
       #   BETTER_AUTH_TRUSTED_ORIGINS=https://gitea-mirror.example.com
+      # Path-prefix deployments (e.g. /mirror) are supported at runtime via BASE_URL.
       
       # === CORE SETTINGS ===
       # These are technically required but have working defaults
@@ -29,6 +30,7 @@ services:
       - DATABASE_URL=file:data/gitea-mirror.db
       - HOST=0.0.0.0
       - PORT=4321
+      - BASE_URL=${BASE_URL:-/}
       - PUBLIC_BETTER_AUTH_URL=${PUBLIC_BETTER_AUTH_URL:-http://localhost:4321}
       # Optional concurrency controls (defaults match in-app defaults)
       # If you want perfect ordering of issues and PRs, set these at 1
@@ -36,7 +38,11 @@ services:
       - MIRROR_PULL_REQUEST_CONCURRENCY=${MIRROR_PULL_REQUEST_CONCURRENCY:-5}
       
     healthcheck:
-      test: ["CMD", "wget", "--no-verbose", "--tries=3", "--spider", "http://localhost:4321/api/health"]
+      test:
+        [
+          "CMD-SHELL",
+          "BASE=\"${BASE_URL:-/}\"; if [ \"$${BASE}\" = \"/\" ]; then BASE=\"\"; else BASE=\"$${BASE%/}\"; fi; wget --no-verbose --tries=3 --spider \"http://localhost:4321$${BASE}/api/health\"",
+        ]
       interval: 30s
       timeout: 10s
       retries: 5