Copilot instructions and build/test skills (#2444)

* Add copilot instructions and skills for build and tests.

* Add dev-server skill.

* Auth Util changes to fix Entra login while running from copilot.

* Fix lint issue.

.github/skills/run-unit-tests/SKILL.md

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+---
+name: run-unit-tests
+description: Run unit tests for the Cosmos Explorer project. Use this skill when asked to run tests, check test results, or debug test failures.
+allowed-tools: shell
+---
+
+# Test Skill
+
+Use the following commands to run unit tests for the Cosmos Explorer project.
+
+## Pre-Test: Check Dependencies
+
+Before running tests, check whether `npm install` needs to be run:
+
+```bash
+if [ ! -d node_modules ] || [ package.json -nt node_modules ] || [ package-lock.json -nt node_modules ]; then
+  npm install
+fi
+```
+
+On Windows PowerShell:
+
+```powershell
+if (-not (Test-Path node_modules) -or
+    (Get-Item package.json).LastWriteTime -gt (Get-Item node_modules).LastWriteTime -or
+    (Get-Item package-lock.json).LastWriteTime -gt (Get-Item node_modules).LastWriteTime) {
+    npm install
+}
+```
+
+Always run this check before proceeding with any test command.
+
+## Run All Unit Tests
+
+Run the full test suite with coverage:
+
+```bash
+npm test
+```
+
+This clears the `coverage/` directory and runs Jest with coverage collection enabled.
+
+## Run a Single Test File
+
+Run a specific test file without coverage (faster):
+
+```bash
+npm run test:file -- path/to/file.test.ts
+```
+
+## Run Tests in Debug Mode
+
+Run tests serially (useful for debugging flaky or interdependent tests):
+
+```bash
+npm run test:debug
+```
+
+## Run Tests Matching a Pattern
+
+Run only tests whose names match a pattern:
+
+```bash
+npx jest --coverage=false --testPathPattern="SomeComponent"
+```
+
+## Guidelines
+
+- When asked to simply "run tests" or "test", run `npm test` for the full suite.
+- When asked to test a specific file or component, use `npm run test:file -- <path>`.
+- When debugging test failures, use `npm run test:debug` to run serially.
+- Unit test files live adjacent to source files (`Foo.test.ts` next to `Foo.ts` in `src/`).
+- Tests use **Jest** with `jest-environment-jsdom`.
+- Use `@testing-library/react` for new component tests. Do not use Enzyme for new tests.
+- Use Jest built-in mocking, not sinon.js.
+- Coverage thresholds are enforced globally: branches 25%, functions 24%, lines 28%, statements 28%.
+- If tests fail, read the error output carefully. Common issues include:
+  - **Snapshot mismatches**: Review the diff. If the change is intentional, update snapshots with `npx jest --updateSnapshot`.
+  - **Mock issues**: Ensure mocks are set up correctly and reset between tests.
+  - **Import errors**: Check that module name mappings in `jest.config.js` are correct.
+  - **Type errors in tests**: Run `npm run compile` to check for TypeScript issues.