Remove dead exports found by knip

- Un-export HOMEBREW_COMMANDS, systemSetupHost, ToolKind, BinaryArchitecture,
  HopperDiagnostic -- only consumed within their own files
- Remove unused HopperUnavailableError class (never instantiated)
- Reformat knip.json entry/project arrays to multi-line

src/application/Setup.ts

@@ -143,7 +143,7 @@ export const runSetup = async (
 };
 
 /** Production setup effects for macOS, Homebrew, JSON MCP clients, and the canonical skill directory. */
-export const systemSetupHost = (): SetupHost => {
+const systemSetupHost = (): SetupHost => {
   const doctorHost = systemDoctorHost();
   return {
     platform: process.platform,

src/application/homebrew.ts

@@ -1,5 +1,5 @@
 /** Standard executable names and locations used to discover Homebrew. */
-export const HOMEBREW_COMMANDS = [
+const HOMEBREW_COMMANDS = [
   "brew",
   "/opt/homebrew/bin/brew",
   "/usr/local/bin/brew",