feat(auth): configure Spring Session JDBC (fa_session, 8h idle, SameSite=strict)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/resources/application-dev.yaml

@@ -1,6 +1,11 @@
 spring:
   jpa:
     show-sql: true
+  session:
+    cookie:
+      # Dev runs over HTTP (port 5173 → 8080); Secure=true would prevent the
+      # cookie from being sent on plain HTTP. Override to false for local dev only.
+      secure: false
 
 springdoc:
   api-docs:

backend/src/main/resources/application.yaml

@@ -38,6 +38,19 @@ spring:
           starttls:
             enable: true
 
+spring:
+  session:
+    store-type: jdbc
+    timeout: 28800s  # 8 h idle timeout (MaxInactiveIntervalInSeconds)
+    jdbc:
+      initialize-schema: never  # Flyway owns schema creation (V67)
+    cookie:
+      name: fa_session
+      same-site: strict
+      http-only: true
+      # secure: true is the default when forward-headers-strategy detects HTTPS behind Caddy.
+      # application-dev.yaml overrides this to false for local HTTP dev.
+
 server:
   # Behind Caddy/reverse proxy: trust X-Forwarded-{Proto,For,Host} so that
   # request.getScheme(), redirect URLs, and Spring Session "Secure" cookies