feat(plugin): support multi-format manifest sources

examples/plugins/mc-auth-proxy/manifest.yaml

@@ -0,0 +1,113 @@
+# Human-maintained plugin manifest. Build packages normalize this into manifest.json.
+schema_version: mc-gateway.plugin/v1
+id: mc-auth-proxy
+name: Minecraft Auth Proxy
+version: 0.1.0
+description: Protocol-proxy example that owns Minecraft login handling and returns a stable fixture disconnect.
+artifact_type: binary
+runtime:
+  type: go-plugin
+  entry: plugin.so
+  entry_symbol: Plugin
+api_version: plugin-api/v1
+sdk_module: github.com/tursom/mc-gateway/plugin/api
+sdk_module_version: v0.1.0
+go_version: go1.24.0
+go_os: linux
+go_arch: amd64
+extension_points:
+  - type: hook
+    key: upstream.connect/v1
+capabilities:
+  upstream_connect:
+    mode: protocol-proxy
+  minecraft:
+    protocol_versions:
+      min: 47
+      max: 767
+      tested:
+        - 47
+        - 760
+        - 763
+        - 767
+      unsupported_policy: kick
+    states:
+      status: transparent
+      login: handled
+      configuration: transparent
+      play: transparent
+    auth_modes:
+      - fixture
+    forwarding:
+      supported:
+        - none
+        - velocity-modern
+      default: none
+      requires_secret: false
+    unsupported_policy: kick
+    modded:
+      forge: transparent
+      fabric: transparent
+      fml: unsupported
+      unknown: pass
+runtime_limits:
+  handler_timeout_ms: 3000
+  initial_write_timeout_ms: 1000
+events:
+  - name: auth.success
+    fields:
+      - result
+      - mode
+  - name: auth.failure
+    fields:
+      - result
+      - mode
+custom_metrics:
+  - name: auth.attempts
+    type: counter
+    labels:
+      - result
+      - mode
+external_dependencies:
+  - name: backend
+    endpoint: tcp://
+    purpose: auth
+    required: true
+    timeout: 3s
+    retry: 0
+    fail_policy: fail_closed
+    data_classes:
+      - operational
+background_tasks:
+  - id: profile-cache-gc
+    name: Profile cache GC
+    mode: manual
+    manual: true
+    timeout: 1s
+data_stores:
+  - name: profile-cache
+    schema_version: 1
+    data_class: profile_cache
+    quota_bytes: 1048576
+    retention: 24h
+    exportable: false
+file_stores:
+  - namespace: cache
+    data_class: profile_cache
+    quota_bytes: 1048576
+    retention: 24h
+  - namespace: diagnostic
+    data_class: diagnostic
+    quota_bytes: 1048576
+    retention: 24h
+config_schema:
+  type: object
+  properties:
+    match_host:
+      type: string
+    fixture_accept:
+      type: boolean
+    disconnect_message:
+      type: string
+    backend:
+      type: string