fix(env): address P1-P3 review items from code review

- P1: Fix bash completion $cliproxy_profiles scoping — inline profiles
  in env block since variable is only defined at COMP_CWORD=1 scope
- P2: Detect account-based profiles and show specific error message
  instead of generic "not found"
- P2: Show `ccs migrate` hint when unified mode is disabled and settings
  profile resolution fails
- P2: transformToOpenAI omits empty entries at transform time instead of
  relying on output filter (removes fragile coupling)
- P3: Add zsh and auto to --shell completions across all 4 shells; map
  --shell zsh to bash in command handler since syntax is identical
- P3: Auto-detect PowerShell from SHELL containing pwsh on non-Windows
- Tests: 33 pass (+1 pwsh detection test, updated transform assertions)

tests/unit/commands/env-command.test.ts

@@ -60,6 +60,11 @@ describe('env-command', () => {
       process.env['SHELL'] = '/bin/bash';
       expect(detectShell('invalid')).toBe('bash');
     });
+
+    it('auto-detects powershell from SHELL containing pwsh', () => {
+      process.env['SHELL'] = '/usr/local/bin/pwsh';
+      expect(detectShell('auto')).toBe('powershell');
+    });
   });
 
   describe('formatExportLine', () => {
@@ -128,11 +133,7 @@ describe('env-command', () => {
     it('handles missing source vars gracefully', () => {
       const result = transformToOpenAI({});
 
-      expect(result).toEqual({
-        OPENAI_API_KEY: '',
-        OPENAI_BASE_URL: '',
-        LOCAL_ENDPOINT: '',
-      });
+      expect(result).toEqual({});
     });
 
     it('only extracts relevant vars', () => {
@@ -143,7 +144,7 @@ describe('env-command', () => {
         DISABLE_TELEMETRY: '1',
       });
 
-      // Should only have 3 keys (no OPENAI_MODEL when ANTHROPIC_MODEL absent)
+      // OPENAI_API_KEY + OPENAI_BASE_URL + LOCAL_ENDPOINT (no OPENAI_MODEL when ANTHROPIC_MODEL absent)
       expect(Object.keys(result)).toHaveLength(3);
       expect(result['ANTHROPIC_MAX_TOKENS']).toBeUndefined();
     });