Mint short links on piha.lc / beta.piha.li (#12)

## Summary
- Point `SHORTENER_BASE_URL` at `https://piha.lc` (prod) and `https://beta.piha.li` (beta).
- Stop documenting `shortener.aimloperations.com` as the mint host.

Closes #11.

Depends on url_shortening_service serving `/api/` on the short host.

## Test plan
- [ ] Set `SHORTENER_BASE_URL=https://beta.piha.li` and matching token in beta env
- [ ] Compose a campaign SMS and confirm mint hits beta.piha.li (not shortener-beta)
- [ ] Body contains `https://beta.piha.li/<code>`

Reviewed-on: #12

.env.prod.example

@@ -88,10 +88,10 @@ OLLAMA_MODEL=llama3.2
 OLLAMA_TIMEOUT_SECONDS=120
 
 # URL shortener — mint short links for campaign SMS / email / postcard QR.
-# POST /api/links/ on the API host. Recipients hit https://piha.li/<code>.
+# POST /api/links/ on the same host phones hit. Recipients use https://piha.lc/<code>.
 # Token must match SHORTENER_API_TOKENS on url_shortening_service (name:secret).
 # Generate: python -c "import secrets; print(secrets.token_urlsafe(32))"
-SHORTENER_BASE_URL=https://shortener.aimloperations.com
+SHORTENER_BASE_URL=https://piha.lc
 SHORTENER_API_TOKEN=monica:replace-me
 
 # Nominatim address suggest (server-side proxy only; not called from browser)
@@ -130,5 +130,5 @@ GUNICORN_BIND=0.0.0.0:8000
 # OLLAMA_BASE_URL=http://10.0.0.128:11434
 # NOMINATIM_BASE_URL=http://10.0.0.128:8089
 # NOMINATIM_COUNTRY_CODES=us
-# SHORTENER_BASE_URL=https://shortener-beta.aimloperations.com
+# SHORTENER_BASE_URL=https://beta.piha.li
 # SHORTENER_API_TOKEN=monica:replace-with-a-different-token