Add UI-driven integration tests with vscode-extension-tester

Add test/ui/extension.test.ts (7 tests) using ExTester + Selenium
WebDriver to exercise the real VS Code UI:

- Status bar: verify Patchloom item appears with correct text
- Show Status: invoke command, verify notification appears
- Open Settings: invoke command, verify settings editor opens
- Configure MCP: invoke command, verify quick pick or warning appears
- Quick Action: invoke command, verify action picker or warning appears
- Configuration changes: verify settings editor can find showStatusBar

Infrastructure:
- Add vscode-extension-tester and @types/mocha as devDependencies
- Add tsconfig.uitest.json for UI test compilation
- Add npm run test:ui script (not part of npm run check)
- Add out-uitest/ and tsconfig.uitest.json to .vscodeignore

UI tests run separately from the fast test suite since they launch a
full VS Code window with WebDriver. Run with: npm run test:ui

Closes #18

Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>

Author: SebTardif

.gitignore

@@ -1,5 +1,6 @@
 node_modules/
 out/
 out-test/
+out-uitest/
 *.vsix
 .vscode-test/

.vscodeignore

@@ -3,7 +3,9 @@
 src/**
 test/**
 out-test/**
+out-uitest/**
 tsconfig.json
 tsconfig.test.json
+tsconfig.uitest.json
 .github/**
 **/*.tsbuildinfo