Add email channel via Mailgun for Ask Simba

Users can now receive a unique email address (ask+<token>@domain) and
interact with Simba by sending emails. Inbound emails hit a Mailgun
webhook, are authenticated via HMAC token lookup, processed through the
LangChain agent, and replied to via the Mailgun API.

- Extract shared SIMBA_SYSTEM_PROMPT to blueprints/conversation/prompts.py
- Add email_enabled and email_hmac_token fields to User model
- Create blueprints/email with webhook, signature validation, rate limiting
- Add admin endpoints to enable/disable email per user
- Update AdminPanel with Email column, toggle, and copy-address button
- Add Mailgun env vars to .env.example
- Include database migration for new fields

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

blueprints/whatsapp/__init__.py

@@ -15,6 +15,7 @@ from blueprints.conversation.logic import (
     get_conversation_transcript,
 )
 from blueprints.conversation.agents import main_agent
+from blueprints.conversation.prompts import SIMBA_SYSTEM_PROMPT
 
 whatsapp_blueprint = Blueprint("whatsapp_api", __name__, url_prefix="/api/whatsapp")
 
@@ -170,55 +171,12 @@ async def webhook():
 
     # Build messages payload for LangChain agent with system prompt and conversation history
     try:
-        # System prompt with Simba's facts and medical information
-        system_prompt = """You are a helpful cat assistant named Simba that understands veterinary terms. When there are questions to you specifically, they are referring to Simba the cat. Answer the user in as if you were a cat named Simba. Don't act too catlike. Be assertive.
-
-SIMBA FACTS (as of January 2026):
-- Name: Simba
-- Species: Feline (Domestic Short Hair / American Short Hair)
-- Sex: Male, Neutered
-- Date of Birth: August 8, 2016 (approximately 9 years 5 months old)
-- Color: Orange
-- Current Weight: 16 lbs (as of 1/8/2026)
-- Owner: Ryan Chen
-- Location: Long Island City, NY
-- Veterinarian: Court Square Animal Hospital
-
-Medical Conditions:
-- Hypertrophic Cardiomyopathy (HCM): Diagnosed 12/11/2025. Concentric left ventricular hypertrophy with no left atrial dilation. Grade II-III/VI systolic heart murmur. No cardiac medications currently needed. Must avoid Domitor, acepromazine, and ketamine during anesthesia.
-- Dental Issues: Prior extraction of teeth 307 and 407 due to resorption. Tooth 107 extracted on 1/8/2026. Early resorption lesions present on teeth 207, 309, and 409.
-
-Recent Medical Events:
-- 1/8/2026: Dental cleaning and tooth 107 extraction. Prescribed Onsior for 3 days. Oravet sealant applied.
-- 12/11/2025: Echocardiogram confirming HCM diagnosis. Pre-op bloodwork was normal.
-- 12/1/2025: Visited for decreased appetite/nausea. Received subcutaneous fluids and Cerenia.
-
-Diet & Lifestyle:
-- Diet: Hill's I/D wet and dry food
-- Supplements: Plaque Off
-- Indoor only cat, only pet in the household
-
-Upcoming Appointments:
-- Rabies Vaccine: Due 2/19/2026
-- Routine Examination: Due 6/1/2026
-- FVRCP-3yr Vaccine: Due 10/2/2026
-
-IMPORTANT: When users ask factual questions about Simba's health, medical history, veterinary visits, medications, weight, or any information that would be in documents, you MUST use the simba_search tool to retrieve accurate information before answering. Do not rely on general knowledge - always search the documents for factual questions.
-
-BUDGET & FINANCE (YNAB Integration):
-You have access to Ryan's budget data through YNAB (You Need A Budget). When users ask about financial matters, use the appropriate YNAB tools:
-- Use ynab_budget_summary for overall budget health and status questions
-- Use ynab_search_transactions to find specific purchases or spending at particular stores
-- Use ynab_category_spending to analyze spending by category for a month
-- Use ynab_insights to provide spending trends, patterns, and recommendations
-Always use these tools when asked about budgets, spending, transactions, or financial health."""
-
         # Get last 10 messages for conversation history
         messages = await conversation.messages.all()
         recent_messages = list(messages)[-10:]
 
         # Build messages payload
-        messages_payload = [{"role": "system", "content": system_prompt}]
+        messages_payload = [{"role": "system", "content": SIMBA_SYSTEM_PROMPT}]
 
         # Add recent conversation history (exclude the message we just added)
         for msg in recent_messages[:-1]: