feat: migrate email send to V3 action; deprecate api.py legacy endpoints

- Add /v3/action/email/send router (api_v3_actions_email.py) replacing /util/email/send
- Disable util_email router in registry; register new email action router
- Mark /api/request_jwt and /api/temp_token as deprecated (TODO: remove)
- Guide: add §8 Email Send Action, mark Axonius section EXPIRED, renumber §9-§11

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

app/routers/api.py

@@ -114,6 +114,8 @@ async def authenticate_passcode(
 
 # --- JWT Request ---
 
+# DEPRECATED — no V3 replacement needed; passcode→JWT is the V3 auth pattern (/api/authenticate_passcode).
+# No frontend references found. Safe to remove after confirming no live traffic. TODO: remove.
 @router.get('/request_jwt', response_model=Resp_Body_Base, dependencies=[Depends(DeprecationParams)])
 async def request_jwt(
         x_aether_signing_key: Optional[str] = Header(None, min_length=22, max_length=22),
@@ -167,6 +169,7 @@ async def request_jwt(
     token = sign_jwt(secret_key=signing_key, public_key=x_aether_api_key, ttl=max_ttl, max_renew=max_renew, **payload)
     return mk_resp(data={ 'jwt': token })
 
+# DEPRECATED — no active use identified. TODO: remove after confirming no live traffic.
 @router.get('/temp_token', response_model=Resp_Body_Base, dependencies=[Depends(DeprecationParams)])
 async def get_api_temp_token(
         x_aether_api_key: Optional[str] = Header(None),