Add RBAC with role-based endpoint authorization and OIDC support

Implement three-phase security upgrade:

Phase 1 - RBAC: Extend JWT with roles claim, populate Spring
GrantedAuthority in filter, enforce role-based access (AGENT for
data/heartbeat/SSE, VIEWER+ for search/diagrams, OPERATOR+ for
commands, ADMIN for user management). Configurable JWT secret via
CAMELEER_JWT_SECRET env var for token persistence across restarts.

Phase 2 - User persistence: ClickHouse users table with
ReplacingMergeTree, UserRepository interface + ClickHouse impl,
UserAdminController for CRUD at /api/v1/admin/users. Local login
upserts user on each authentication.

Phase 3 - OIDC: Token exchange flow where SPA sends auth code,
server exchanges it server-side (keeping client_secret secure),
validates id_token via JWKS, resolves roles (DB override > OIDC
claim > default), issues internal JWT. Conditional on
CAMELEER_OIDC_ENABLED=true. Uses oauth2-oidc-sdk for standards
compliance.

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

cameleer3-server-app/pom.xml

@@ -75,6 +75,11 @@
             <artifactId>nimbus-jose-jwt</artifactId>
             <version>9.47</version>
         </dependency>
+        <dependency>
+            <groupId>com.nimbusds</groupId>
+            <artifactId>oauth2-oidc-sdk</artifactId>
+            <version>11.23.1</version>
+        </dependency>
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-test</artifactId>