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_system_prompt.py

@@ -0,0 +1,28 @@
+"""Tests for the unified persona system prompt.
+
+The persona should match the user's configured wake word so renaming the
+wake word to e.g. "Friday" produces a butler named Friday, not one still
+hardcoded to Jarvis.
+"""
+
+from jarvis.system_prompt import build_system_prompt
+
+
+class TestBuildSystemPrompt:
+    def test_default_name_is_jarvis(self):
+        prompt = build_system_prompt()
+        assert "named Jarvis" in prompt
+
+    def test_custom_name_replaces_jarvis(self):
+        prompt = build_system_prompt("Friday")
+        assert "named Friday" in prompt
+        assert "named Jarvis" not in prompt
+
+    def test_lowercase_wake_word_is_capitalised(self):
+        prompt = build_system_prompt("friday".capitalize())
+        assert "named Friday" in prompt
+
+    def test_blank_name_falls_back_to_jarvis(self):
+        assert "named Jarvis" in build_system_prompt("")
+        assert "named Jarvis" in build_system_prompt("   ")
+        assert "named Jarvis" in build_system_prompt(None)  # type: ignore[arg-type]