feat: port CLI, TUI, and launcher from v1.5 into v2 (#1452)

Ports the CLI, TUI, and launcher from v1.5 into v2 behind a single
`mcp-inspector` entrypoint (launcher → web/cli/tui). Includes the
`mcp-inspector --web --dev` launcher fix (Vite alias resolution + prod-server
double-start), the root `postinstall` install cascade with simplified CI, and
spec/AGENTS docs (no-workspaces rationale, Development setup).

Closes #1246.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/cli/__tests__/README.md

@@ -0,0 +1,44 @@
+# CLI Tests
+
+## Running Tests
+
+```bash
+# Run all tests
+npm test
+
+# Run in watch mode (useful for test file changes; won't work on CLI source changes without rebuild)
+npm run test:watch
+
+# Run specific test file
+npm run test:cli          # cli.test.ts
+npm run test:cli-tools   # tools.test.ts
+npm run test:cli-headers # headers.test.ts
+npm run test:cli-metadata # metadata.test.ts
+```
+
+## Test Files
+
+- `cli.test.ts` - Basic CLI functionality: CLI mode, environment variables, config files, resources, prompts, logging, transport types
+- `tools.test.ts` - Tool-related tests: Tool discovery, JSON argument parsing, error handling, prompts
+- `headers.test.ts` - Header parsing and validation
+- `metadata.test.ts` - Metadata functionality: General metadata, tool-specific metadata, parsing, merging, validation
+
+## Helpers
+
+The `helpers/` directory contains shared utilities:
+
+- `cli-runner.ts` - Spawns CLI as subprocess and captures output
+- `test-mcp-server.ts` - Standalone stdio MCP server script for stdio transport testing
+- `instrumented-server.ts` - In-process MCP test server for HTTP/SSE transports with request recording
+- `assertions.ts` - Custom assertion helpers for CLI output validation
+- `fixtures.ts` - Test config file generators and temporary directory management
+
+## Notes
+
+- Tests run in parallel across files (Vitest default)
+- Tests within a file run sequentially (we have isolated config files and ports, so we could get more aggressive if desired)
+- Config files use `crypto.randomUUID()` for uniqueness in parallel execution
+- HTTP/SSE servers use dynamic port allocation to avoid conflicts
+- Coverage is not used because much of the code that we want to measure is run by a spawned process, so it can't be tracked by Vitest
+- /sample-config.json is no longer used by tests - not clear if this file serves some other purpose so leaving it for now
+- All tests now use built-in MCP test servers, there are no external dependencies on servers from a registry