feat(dashboard): live-editable bot prompt via popup (view/edit/save)

Adds a persisted, runtime-editable system prompt. The brain reads the persona
on every turn (prompt_store.get_persona), so a dashboard edit applies to the
next reply with no restart; blank clears the override back to the built-in
PERSONA. New endpoints GET/POST /api/prompt, and a reusable modal popup
(뒤로가기 + 수정/저장) that later white/blacklist features will share.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

wsai/backends/claude.py

@@ -24,6 +24,7 @@ import os
 import time
 
 from ..interfaces import Frame, Reply, ScreenObservation
+from ..prompt_store import get_persona
 
 # Claude Code OAuth tokens only answer when the first system block is exactly
 # this identity string; the real persona/instructions go in later blocks.
@@ -148,10 +149,12 @@ class ClaudeBrain:
         screen_note = f"[지금 화면] {screen.text}\n\n" if screen else "[지금 화면] (아직 못 읽음)\n\n"
         msgs.append({"role": "user", "content": screen_note + user_text})
         client = self._auth.client()
+        # Read the persona live each turn so a dashboard edit applies immediately
+        # (falls back to the built-in PERSONA when no override is saved).
         resp = await client.messages.create(
             model=self.model,
             max_tokens=400,
-            system=self._auth.system(self.PERSONA),
+            system=self._auth.system(get_persona(self.PERSONA)),
             messages=msgs,
         )
         text = "".join(b.text for b in resp.content if b.type == "text")