Add per-service system prompts with AI Settings tab view

Each feature service owns its system prompt in its config JSON on the
shared volume. The AI Settings page now has General and System Prompts
tabs — admins can view and edit any service's prompts at runtime with
changes taking effect within 30 s (config cache TTL).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

features/doc-service/app/services/config_reader.py

@@ -14,8 +14,39 @@ from pathlib import Path
 
 from app.core.config import settings
 
+_DEFAULT_SYSTEM_PROMPT = (
+    "You are a financial document analysis assistant. "
+    "Given the text extracted from a PDF document, return ONLY a JSON object "
+    "with no markdown, no code fences, and no explanation."
+)
+
+_DEFAULT_USER_TEMPLATE = (
+    'Analyze the following document text and return a JSON object with exactly these keys:\n'
+    'title (a short, descriptive human-readable title for this document, e.g. "ACME Corp Invoice April 2026", "Office Supplies Receipt", "Q1 Flower Delivery Order"),\n'
+    'document_type (one of: invoice, bill, receipt, order, expense, revenue, unknown),\n'
+    'total_amount (string or null),\n'
+    'currency (string or null),\n'
+    'vendor_name (string or null),\n'
+    'customer_name (string or null),\n'
+    'billing_address (string or null),\n'
+    'customer_address (string or null),\n'
+    'invoice_number (string or null),\n'
+    'invoice_date (string or null),\n'
+    'due_date (string or null),\n'
+    'tags (array of short keyword strings describing the document),\n'
+    'line_items (array of objects, each with keys: description, amount),\n'
+    'suggested_categories (array of 2 to 5 short category name strings a user might want to file this document under, e.g. "Utilities", "Travel", "Software Subscriptions", "Client Invoices").\n'
+    '\n'
+    'Document text:\n'
+    '{text}'
+)
+
 _DEFAULT_CONFIG: dict = {
     "documents": {"max_pdf_bytes": 20 * 1024 * 1024},
+    "system_prompts": {
+        "system": _DEFAULT_SYSTEM_PROMPT,
+        "user_template": _DEFAULT_USER_TEMPLATE,
+    },
 }
 
 _cache: dict | None = None