fix(dev): default port :8080 → :8090

Unblock local dev: Keycloak owns :8080, so tenant-registry shifts to :8090. Prod is functionally unchanged.

Refs: M5.1

.env.example

@@ -0,0 +1,11 @@
+# tenant-registry — local dev environment.
+#
+# Copy to .env.local (gitignored) and edit. The service reads env vars
+# directly via internal/config; this file is just documentation.
+
+APP_ENV=dev
+ADDR=:8090
+KEYCLOAK_ISSUER=http://localhost:8080/realms/breakpilot-dev
+
+# Postgres DSN — unused by the skeleton (in-memory store). Wired up in M4.1.
+# DATABASE_URL=postgres://platform:platform-dev-pass@localhost:5432/platform?sslmode=disable