feat(public): version/health surfacing for the app first-run probe

Expose a small backend identity/version descriptor (§8.4 of the Android plan)
so a client can positively recognize a Runic Gateway backend on first-run and
run a version-mismatch guard, instead of inferring from an incidental shape.

- New config/version.js: { service: 'runic-gateway', api: 'v1', server: <pkg> }.
- GET /public/status now includes a `version` block (the app already calls this
  on first-run, so it gets identity + version in one round trip).
- New GET /public/version: a lightweight, DB-free identity endpoint — the
  canonical target for the version guard and a cheap liveness check.
- Swagger: PublicVersion schema + version on PublicStatus; /version annotated.
- test/publicVersion.test.js covers the config shape and the DB-free 200.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NgyHnrNa8WwG3doxvxjuCr

server/src/router/v1/public/public.routes.js

@@ -22,10 +22,18 @@ publicRouter.get(
   '/status',
   // #swagger.tags = ['Public']
   // #swagger.summary = 'Site mode / status'
-  // #swagger.description = 'Current site mode (live or maintenance) so the client can show the maintenance page.'
+  // #swagger.description = 'Current site mode (live or maintenance) so the client can show the maintenance page, plus a version block (service id + API/server versions) for a client first-run probe and version-mismatch guard.'
   /* #swagger.responses[200] = { description: 'Site status', content: { "application/json": { schema: { $ref: "#/components/schemas/PublicStatus" } } } } */
   ctrl.getStatus,
 )
+publicRouter.get(
+  '/version',
+  // #swagger.tags = ['Public']
+  // #swagger.summary = 'Backend identity + version'
+  // #swagger.description = 'Lightweight, DB-free descriptor of this backend: a stable service id and the API/server versions. A client uses it to recognize a Runic Gateway backend on first-run and to run a version-mismatch guard. Doubles as a cheap liveness check.'
+  /* #swagger.responses[200] = { description: 'Backend version', content: { "application/json": { schema: { $ref: "#/components/schemas/PublicVersion" } } } } */
+  ctrl.getVersion,
+)
 publicRouter.post(
   '/contact',
   // #swagger.tags = ['Public']