Use ClaudeBinaryResolver instead of null binary path in extension services
(McpHealthDiagnosticsService, PluginInstallService, McpInstallService).
Packaged Electron on macOS has minimal PATH — bare `claude` lookup fails
with ENOENT. Now all CLI calls resolve the binary via ClaudeBinaryResolver
which checks PATH, NVM, standard install dirs and login shell env.
- Add buildEnrichedEnv() helper for child process env (PATH, HOME, USERPROFILE)
- Add stale cache re-verification with 30s TTL in ClaudeBinaryResolver
- Guard execCli() against null binaryPath with explicit error
- Replace projectPath.startsWith('/') with path.isAbsolute() for Windows
- Extract CLI_NOT_FOUND_MARKER/MESSAGE constants for consistent error detection
- Show amber info banner instead of red error when CLI not installed
