Migrate permission system from MCP file-based to stdio-based

Replace MCP permission server with stdio-based permission flow that
communicates directly with Claude CLI via stdin/stdout. This simplifies
the architecture and fixes permission expiration issues.

Key changes:
- Use --permission-prompt-tool stdio and --input-format stream-json
- Handle control_request messages for permission prompts
- Send control_response via stdin to approve/deny
- Check local permissions for auto-approval of pre-approved tools
- Only expire pending permissions when VS Code restarts, not panel close

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/ui-styles.ts

@@ -302,6 +302,12 @@ const styles = `
         border: 1px solid rgba(231, 76, 60, 0.3);
     }
 
+    .permission-decision.expired {
+        background-color: rgba(128, 128, 128, 0.15);
+        color: var(--vscode-descriptionForeground);
+        border: 1px solid rgba(128, 128, 128, 0.3);
+    }
+
     .permission-decided {
         opacity: 0.7;
         pointer-events: none;
@@ -321,6 +327,11 @@ const styles = `
         background-color: var(--vscode-inputValidation-errorBackground);
     }
 
+    .permission-decided.expired {
+        border-color: var(--vscode-panel-border);
+        background-color: rgba(128, 128, 128, 0.05);
+    }
+
     /* Permissions Management */
     .permissions-list {
         max-height: 300px;