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/test_memory_viewer_graph_api.py

@@ -0,0 +1,75 @@
+"""Tests for the memory viewer graph HTTP API.
+
+Focused on the preset-protection contract: the seeded fixed branches and
+root must not be deletable through the public DELETE endpoint, and the
+``/api/graph/presets`` endpoint must surface the same set the backend
+guards (single source of truth for the JS UI).
+"""
+
+from __future__ import annotations
+
+import pytest
+
+try:
+    import flask  # noqa: F401
+
+    _HAS_FLASK = True
+except ImportError:
+    _HAS_FLASK = False
+
+from src.jarvis.memory.graph import FIXED_BRANCH_IDS, GraphMemoryStore
+
+
+@pytest.mark.unit
+@pytest.mark.skipif(not _HAS_FLASK, reason="Flask not available")
+class TestGraphPresetProtection:
+    """End-to-end coverage for non-deletable preset nodes via Flask."""
+
+    @pytest.fixture(autouse=True)
+    def setup_app(self, tmp_path):
+        from src.desktop_app import memory_viewer
+
+        db_path = str(tmp_path / "test.db")
+        store = GraphMemoryStore(db_path)
+
+        # Inject the store directly so we don't need to patch _get_db_path.
+        memory_viewer._graph_store = store
+
+        memory_viewer.app.config["TESTING"] = True
+        self.client = memory_viewer.app.test_client()
+        self.store = store
+
+        yield
+
+        store.close()
+        memory_viewer._graph_store = None
+
+    def test_presets_endpoint_lists_root_and_fixed_branches(self):
+        resp = self.client.get("/api/graph/presets")
+        assert resp.status_code == 200
+        ids = set(resp.get_json()["ids"])
+        assert ids == {"root", *FIXED_BRANCH_IDS}
+
+    def test_delete_root_returns_400(self):
+        resp = self.client.delete("/api/graph/node/root")
+        assert resp.status_code == 400
+        assert "root" in resp.get_json()["error"].lower()
+        assert self.store.get_node("root") is not None
+
+    def test_delete_fixed_branch_returns_400(self):
+        for branch_id in FIXED_BRANCH_IDS:
+            resp = self.client.delete(f"/api/graph/node/{branch_id}")
+            assert resp.status_code == 400, (
+                f"DELETE on fixed branch {branch_id!r} must be rejected"
+            )
+            assert resp.get_json()["error"] == "Cannot delete preset branch"
+            assert self.store.get_node(branch_id) is not None
+
+    def test_delete_user_created_node_succeeds(self):
+        node = self.store.create_node(
+            name="Scratch", description="d", parent_id="root"
+        )
+        resp = self.client.delete(f"/api/graph/node/{node.id}")
+        assert resp.status_code == 200
+        assert resp.get_json() == {"success": True}
+        assert self.store.get_node(node.id) is None