fix: extract Edge Functions base URL into a single shared SQL function

notify_booking_created() and notify_inquiry_created() each held their own
literal copy of the local Edge Functions base URL. Introduce
public.edge_functions_base_url() as the single source of truth so Task 9's
production deploy only needs to update one function definition instead of
two independent literals.

supabase/migrations/20260808000003_notify_triggers.sql

@@ -44,17 +44,33 @@ create extension if not exists pg_net with schema extensions;
 -- `extensions.net` as database.schema). Fixed to call `net.http_post`
 -- directly below.
 
+-- Single source of truth for the Edge Functions base URL, used by both
+-- notify_booking_created() and notify_inquiry_created() below. Task 9
+-- (production deploy) MUST update this function's return value to the real
+-- deployed Edge Functions URL (e.g. https://<project-ref>.supabase.co/functions/v1)
+-- when promoting to production. Because both trigger functions call through
+-- this single function rather than each holding their own copy of the
+-- literal, updating this one definition (and re-running the migration or an
+-- equivalent `create or replace function` in production) is sufficient to
+-- repoint both notification paths — there is no second copy to remember to
+-- edit.
+create or replace function public.edge_functions_base_url()
+returns text
+language sql
+immutable
+as $$
+  select 'http://host.docker.internal:54321/functions/v1'
+$$;
+
 create or replace function public.notify_booking_created()
 returns trigger
 language plpgsql
 security definer
 set search_path = ''
 as $$
-declare
-  base_url text := 'http://host.docker.internal:54321/functions/v1';
 begin
   perform net.http_post(
-    url := base_url || '/on-booking-created',
+    url := public.edge_functions_base_url() || '/on-booking-created',
     headers := jsonb_build_object('Content-Type', 'application/json'),
     body := jsonb_build_object('record', to_jsonb(new))
   );
@@ -73,11 +89,9 @@ language plpgsql
 security definer
 set search_path = ''
 as $$
-declare
-  base_url text := 'http://host.docker.internal:54321/functions/v1';
 begin
   perform net.http_post(
-    url := base_url || '/on-inquiry-created',
+    url := public.edge_functions_base_url() || '/on-inquiry-created',
     headers := jsonb_build_object('Content-Type', 'application/json'),
     body := jsonb_build_object('record', to_jsonb(new))
   );