test(ci): improve test isolation readability per review feedback

- Extract NEUTRAL_PROFILE_TYPE constant with JSDoc explaining why
  CCS_PROFILE_TYPE must be neutralised in subprocess env blocks
- Replace 6 bare '' occurrences with the named constant (DRY)
- Group save/delete operations in beforeEach with section comments

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tests/unit/utils/claudecode-env-stripping.test.ts

@@ -152,12 +152,17 @@ describe('CLAUDECODE environment stripping', () => {
   beforeEach(() => {
     spawnCalls.length = 0;
     process.env.CCS_QUIET = '1';
+
+    // Save original env values for restoration in afterEach
     originalCcsHome = process.env.CCS_HOME;
     originalCcsClaudePath = process.env.CCS_CLAUDE_PATH;
     originalDisableAutoUpdater = process.env.DISABLE_AUTOUPDATER;
     originalClaudeConfigDir = process.env.CLAUDE_CONFIG_DIR;
+
+    // Clear CCS-managed env vars that leak from host sessions
     delete process.env.DISABLE_AUTOUPDATER;
     delete process.env.CLAUDE_CONFIG_DIR;
+
     baselineSigintListeners = process.listeners('SIGINT');
     baselineSigtermListeners = process.listeners('SIGTERM');
     baselineSighupListeners = process.listeners('SIGHUP');