Add Discord-native hybrid front-end for Jarvis (bot + bridge)

Transform isair/jarvis into a Discord-controlled voice assistant running on
the Ubuntu VNC desktop, keeping the mature ~39k-line Python brain intact.

- bot/ (Node + bun, discord.js): /자비스 slash commands (ephemeral),
  voice channel join + voice receive/playback, pluggable VNC screen broadcast
  (selfbot live / noVNC / screenshot)
- bridge/ (Python, Flask): wraps jarvis STT + run_reply_engine + Piper TTS
  behind a thin localhost HTTP API
- .env.example, scripts/ (start_bridge/start_bot/dev), README rewrite,
  docs/language-comparison.md and docs/vnc-xfce-setup.md

Language decision: hybrid (Python brain + Node/bun Discord layer) because
Discord blocks bot video; native screen broadcast only works via a Node
selfbot library.

tests/tools/builtin/test_screenshot.py

@@ -0,0 +1,87 @@
+"""Tests for screenshot tool."""
+
+import pytest
+from unittest.mock import Mock, patch
+import sys
+
+from src.jarvis.tools.builtin.screenshot import ScreenshotTool
+from src.jarvis.tools.base import ToolContext
+from src.jarvis.tools.types import ToolExecutionResult
+
+
+class TestScreenshotTool:
+    """Test screenshot tool functionality."""
+
+    def setup_method(self):
+        """Set up test fixtures."""
+        self.tool = ScreenshotTool()
+        self.context = Mock(spec=ToolContext)
+        self.context.user_print = Mock()
+
+    def test_tool_properties(self):
+        """Test tool metadata properties."""
+        assert self.tool.name == "screenshot"
+        assert "capture" in self.tool.description.lower()
+        assert self.tool.inputSchema["type"] == "object"
+        assert self.tool.inputSchema["required"] == []
+
+    @patch('shutil.which')
+    @patch('subprocess.run')
+    def test_run_success(self, mock_run, mock_which):
+        """Test successful screenshot capture with inlined OCR logic."""
+        # Lightweight stubs so dynamic imports succeed without heavy deps
+        class _StubImgCtx:
+            def __enter__(self):
+                return self
+            def __exit__(self, *a):
+                return False
+        class _StubImage:
+            @staticmethod
+            def open(*a, **k):
+                return _StubImgCtx()
+
+        sys.modules['pytesseract'] = type('StubTess', (), {
+            'image_to_string': staticmethod(lambda *a, **k: 'Sample OCR text')
+        })
+        sys.modules['PIL'] = type('StubPIL', (), {'Image': _StubImage})
+        sys.modules['PIL.Image'] = _StubImage
+
+        # Indicate tools exist
+        def which_side_effect(name):
+            return f"/usr/bin/{name}" if name in ("screencapture", "tesseract") else None
+        mock_which.side_effect = which_side_effect
+
+        mock_proc = Mock()
+        mock_proc.returncode = 0
+        mock_run.return_value = mock_proc
+
+        with patch('tempfile.mkdtemp', return_value='/tmp/jarvis_ocr_test'), \
+             patch('os.path.exists', return_value=True), \
+             patch('os.remove'), \
+             patch('os.rmdir'):
+            result = self.tool.run({}, self.context)
+
+        assert isinstance(result, ToolExecutionResult)
+        assert result.success is True
+        assert result.reply_text == 'Sample OCR text'
+        self.context.user_print.assert_called()
+
+    @patch('shutil.which')
+    @patch('subprocess.run')
+    def test_run_empty_ocr(self, mock_run, mock_which):
+        """Test screenshot with empty OCR result (tesseract missing)."""
+        # screencapture present, tesseract missing
+        def which_side_effect(name):
+            if name == 'screencapture':
+                return '/usr/bin/screencapture'
+            return None
+        mock_which.side_effect = which_side_effect
+        mock_proc = Mock(); mock_proc.returncode = 0; mock_run.return_value = mock_proc
+        with patch('tempfile.mkdtemp') as mock_tmp, \
+             patch('os.path.exists') as mock_exists:
+            mock_tmp.return_value = '/tmp/jarvis_ocr_test'
+            mock_exists.return_value = True
+            result = self.tool.run({}, self.context)
+        assert isinstance(result, ToolExecutionResult)
+        assert result.success is True
+        assert result.reply_text == ''