feat: move SaaS app to /platform base path, Logto becomes catch-all

Eliminates all Logto path enumeration in Traefik. Routing is now:
- /platform/* → cameleer-saas (SPA + API)
- /server/* → server-ui
- /* (catch-all) → Logto (sign-in, OIDC, assets, everything)

Spring context-path handles backend prefix transparently. No changes
needed in controllers, SecurityConfig, or interceptors.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main/resources/application-test.yml

@@ -1,3 +1,7 @@
+server:
+  servlet:
+    context-path: /platform
+
 spring:
   jpa:
     show-sql: false

src/main/resources/application.yml

@@ -1,3 +1,7 @@
+server:
+  servlet:
+    context-path: /platform
+
 spring:
   application:
     name: cameleer-saas