backend: replace LAST_FULL_PROMPT/LAST_CAT_INTERACTION with unified PROMPT_HISTORY deque

- globals.py: add collections.deque(maxlen=10) PROMPT_HISTORY with _prompt_id_counter
- globals.py: add legacy accessor functions _get_last_fallback_prompt() and _get_last_cat_interaction()
- bot.py: append to PROMPT_HISTORY instead of setting LAST_CAT_INTERACTION, remove 500-char truncation, add guild/channel/model fields
- image_handling.py: same pattern for Cat media responses
- llm.py: append fallback prompts to PROMPT_HISTORY with response filled after LLM reply
- routes/core.py: new GET /prompts and GET /prompts/{id} endpoints, legacy /prompt and /prompt/cat use accessor functions

bot/globals.py

@@ -1,6 +1,7 @@
 # globals.py
 import os
 import discord
+from collections import deque
 from apscheduler.schedulers.asyncio import AsyncIOScheduler
 
 scheduler = AsyncIOScheduler()
@@ -77,16 +78,25 @@ MIKU_NORMAL_AVATAR_URL = None  # Cached CDN URL of the regular Miku pfp (valid e
 
 BOT_USER = None
 
-LAST_FULL_PROMPT = ""
+# Unified prompt history (replaces LAST_FULL_PROMPT and LAST_CAT_INTERACTION)
+# Each entry: {id, source, full_prompt, response, user, mood, guild, channel,
+#              timestamp, model, response_type}
+PROMPT_HISTORY = deque(maxlen=10)
+_prompt_id_counter = 0
 
-# Cheshire Cat last interaction tracking (for Web UI Last Prompt toggle)
-LAST_CAT_INTERACTION = {
-    "full_prompt": "",
-    "response": "",
-    "user": "",
-    "mood": "",
-    "timestamp": "",
-}
+# Legacy accessors for backward compatibility (routes, CLI, etc.)
+# These are computed properties that read from PROMPT_HISTORY
+def _get_last_fallback_prompt():
+    for entry in reversed(PROMPT_HISTORY):
+        if entry.get("source") == "fallback":
+            return entry.get("full_prompt", "")
+    return ""
+
+def _get_last_cat_interaction():
+    for entry in reversed(PROMPT_HISTORY):
+        if entry.get("source") == "cat":
+            return entry
+    return {"full_prompt": "", "response": "", "user": "", "mood": "", "timestamp": ""}
 
 # Persona Dialogue System (conversations between Miku and Evil Miku)
 LAST_PERSONA_DIALOGUE_TIME = 0  # Timestamp of last dialogue for cooldown