fix: #167 — show-command and show-tool now accept --output-format flag; CLI parity with session-lifecycle family

Closes the inspect-capability parity gap: show-command and show-tool were
the only discovery/inspection CLI commands lacking --output-format support,
making them outliers in the ecosystem that already had unified JSON
contracts across list-sessions, load-session, delete-session, and
flush-transcript (#160/#165/#166).

Concrete additions:

- show-command: --output-format {text,json}
- show-tool: --output-format {text,json}

JSON envelope shape (found case):
  {name, found: true, source_hint, responsibility}

JSON envelope shape (not-found case):
  {name, found: false, error: {kind:'command_not_found'|'tool_not_found',
                               message, retryable: false}}

Exit codes:
  0 = success
  1 = not found

Backward compatibility:
  - Default (no --output-format) is 'text' (unchanged)
  - Text output byte-identical to pre-#167 (three newline-separated lines)

Tests (10 new, test_show_command_tool_output_format.py):
  - TestShowCommandOutputFormat (5): found + not-found in JSON; text mode
    backward compat; text is default
  - TestShowToolOutputFormat (3): found + not-found in JSON; text mode
    backward compat
  - TestShowCommandToolFormatParity (2): both accept same flag choices;
    consistent JSON envelope shape

Full suite: 114 → 124 passing, zero regression.

Closes ROADMAP #167.

Why this matters:
  Before: Claws calling show-command/show-tool had to parse human-readable
  prose output via regex, with no structured error signal.
  After: Same envelope contract as load-session and friends: JSON-first,
  typed errors, machine-parseable.

Related clusters:
  - Session-lifecycle CLI parity family (#160, #165, #166, #167)
  - Machine-readable error contracts (same vein as #162 atomicity + #164
    cancellation state-safety: structured boundaries for orchestration)

src/main.py

@@ -157,8 +157,10 @@ def build_parser() -> argparse.ArgumentParser:
 
     show_command = subparsers.add_parser('show-command', help='show one mirrored command entry by exact name')
     show_command.add_argument('name')
+    show_command.add_argument('--output-format', choices=['text', 'json'], default='text')
     show_tool = subparsers.add_parser('show-tool', help='show one mirrored tool entry by exact name')
     show_tool.add_argument('name')
+    show_tool.add_argument('--output-format', choices=['text', 'json'], default='text')
 
     exec_command_parser = subparsers.add_parser('exec-command', help='execute a mirrored command shim by exact name')
     exec_command_parser.add_argument('name')
@@ -394,16 +396,62 @@ def main(argv: list[str] | None = None) -> int:
     if args.command == 'show-command':
         module = get_command(args.name)
         if module is None:
-            print(f'Command not found: {args.name}')
+            if args.output_format == 'json':
+                import json
+                error_envelope = {
+                    'name': args.name,
+                    'found': False,
+                    'error': {
+                        'kind': 'command_not_found',
+                        'message': f'Unknown command: {args.name}',
+                        'retryable': False,
+                    },
+                }
+                print(json.dumps(error_envelope))
+            else:
+                print(f'Command not found: {args.name}')
             return 1
-        print('\n'.join([module.name, module.source_hint, module.responsibility]))
+        if args.output_format == 'json':
+            import json
+            output = {
+                'name': module.name,
+                'found': True,
+                'source_hint': module.source_hint,
+                'responsibility': module.responsibility,
+            }
+            print(json.dumps(output))
+        else:
+            print('\n'.join([module.name, module.source_hint, module.responsibility]))
         return 0
     if args.command == 'show-tool':
         module = get_tool(args.name)
         if module is None:
-            print(f'Tool not found: {args.name}')
+            if args.output_format == 'json':
+                import json
+                error_envelope = {
+                    'name': args.name,
+                    'found': False,
+                    'error': {
+                        'kind': 'tool_not_found',
+                        'message': f'Unknown tool: {args.name}',
+                        'retryable': False,
+                    },
+                }
+                print(json.dumps(error_envelope))
+            else:
+                print(f'Tool not found: {args.name}')
             return 1
-        print('\n'.join([module.name, module.source_hint, module.responsibility]))
+        if args.output_format == 'json':
+            import json
+            output = {
+                'name': module.name,
+                'found': True,
+                'source_hint': module.source_hint,
+                'responsibility': module.responsibility,
+            }
+            print(json.dumps(output))
+        else:
+            print('\n'.join([module.name, module.source_hint, module.responsibility]))
         return 0
     if args.command == 'exec-command':
         result = execute_command(args.name, args.prompt)