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.

docs/ui/exception-center.md

@@ -0,0 +1,18 @@
+# Exception Center UI (stub)
+
+> Status: BLOCKED — waiting on UI assets/payloads and accessibility guidance (DOCS-EXC-25-005).
+
+## Outline
+1. Overview + imposed rule banner
+2. Navigation and badges
+3. Workflow walkthrough (create, approve, reject)
+4. Accessibility/keyboard shortcuts
+5. Offline considerations (asset packaging, deterministic captures)
+6. Troubleshooting
+
+## Determinism
+- Hash captures/payloads into `docs/ui/SHA256SUMS` once provided.
+- Prefer command-rendered outputs where possible; if screenshots are used, store under `docs/ui/assets/exception-center/` with hashes.
+
+## Assets
+- Screenshots/command-rendered outputs (when provided) will live under `docs/ui/assets/exception-center/` and be hash-listed in `docs/ui/SHA256SUMS`.