feat: search-engine indexing — robots.txt, sitemap.xml, llms.txt, SEO meta

robots.txt (sitemap pointer, /metrics and /scrape/ disallowed),
sitemap.xml (/ and /docs), and llms.txt (site + API summary for LLM
crawlers) served at the domain root. Dashboard head gains title with
keywords, meta description, canonical, Open Graph/Twitter tags,
schema.org WebApplication JSON-LD, theme-color, and an inline SVG
favicon (also silences the /favicon.ico 404).

src/web_api.py

@@ -16,7 +16,7 @@ from typing import Any, Dict, List, Optional
 import requests
 from fastapi import BackgroundTasks, Depends, FastAPI, Header, HTTPException, Query
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import HTMLResponse
+from fastapi.responses import FileResponse, HTMLResponse
 from fastapi.staticfiles import StaticFiles
 
 from .config import Config
@@ -276,6 +276,27 @@ async def root():
     return HTMLResponse(content=DASHBOARD_HTML)
 
 
+# Crawler/indexing files must live at the domain root (served from src/static)
+_STATIC_DIR = os.path.dirname(_DASHBOARD_HTML_PATH)
+
+
+@app.get("/robots.txt", include_in_schema=False)
+async def robots_txt():
+    return FileResponse(os.path.join(_STATIC_DIR, "robots.txt"), media_type="text/plain")
+
+
+@app.get("/llms.txt", include_in_schema=False)
+async def llms_txt():
+    return FileResponse(os.path.join(_STATIC_DIR, "llms.txt"), media_type="text/plain")
+
+
+@app.get("/sitemap.xml", include_in_schema=False)
+async def sitemap_xml():
+    return FileResponse(
+        os.path.join(_STATIC_DIR, "sitemap.xml"), media_type="application/xml"
+    )
+
+
 @app.get("/health", response_model=HealthResponse)
 async def get_health():
     """Get system health status"""