Add unit tests for Router configuration and transport layers

- Implemented tests for RouterConfig, RoutingOptions, StaticInstanceConfig, and RouterConfigOptions to ensure default values are set correctly.
- Added tests for RouterConfigProvider to validate configurations and ensure defaults are returned when no file is specified.
- Created tests for ConfigValidationResult to check success and error scenarios.
- Developed tests for ServiceCollectionExtensions to verify service registration for RouterConfig.
- Introduced UdpTransportTests to validate serialization, connection, request-response, and error handling in UDP transport.
- Added scripts for signing authority gaps and hashing DevPortal SDK snippets.

src/DevPortal/StellaOps.DevPortal.Site/snippets/README.stub

@@ -0,0 +1,4 @@
+# DevPortal SDK Snippets (Wave B placeholder)
+
+Place language-specific snippet packs here when delivered (e.g., `node/`, `python/`, `java/`).
+Keep filenames stable and deterministic; run `tools/devportal/hash-snippets.sh` to update SHA256SUMS.devportal-stubs after drops.