fix(deploy): give migrate the API's client-address settings, and say what Doctor checked

Doctor checks the client-address configuration of the process it runs
in, and operators run it as `migrate`. The proxy overlay set
trusted-proxy mode on `api` only, so Doctor reported "Direct
client-address mode" for an installation that trusts its proxy.

- compose.proxy.yaml defines the three variables once, as a YAML
  anchor, and applies it to both `api` and `migrate`. Rendered with
  `docker compose config`, `api` is unchanged and `migrate` now
  matches it, keeping NODE_EXTRA_CA_CERTS from the base.
- The example deploy/.env sets
  COMPOSE_FILE=compose.yaml:compose.proxy.yaml, as the instance already
  does. Plain `docker compose run --rm migrate ...` in the README then
  runs with the overlay; it used to read compose.yaml alone.
- Every client-address check in Doctor now says it checked the
  environment Doctor runs with, and how to read the running API's own
  value (`docker compose exec api printenv
  EKKLESIA_CLIENT_ADDRESS_MODE`, confirmed to work in the image).
- The deploy README explains why operator commands need the same files
  as the stack.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

deploy/compose.proxy.yaml

@@ -13,6 +13,13 @@
 # its lower half; the proxy (and the tunnel connector, if used) take addresses from the upper half,
 # which Docker never hands to another container.
 
+# Exactly one trusted peer: this proxy. Set from the same variable that fixes the proxy's address,
+# so the two cannot drift apart. These override any value in ekklesia.env.
+x-ekklesia-client-address: &ekklesia-client-address
+  EKKLESIA_CLIENT_ADDRESS_MODE: trusted-proxy
+  EKKLESIA_CLIENT_ADDRESS_HEADER: x-forwarded-for
+  EKKLESIA_CLIENT_ADDRESS_TRUSTED_PROXIES: ${EKKLESIA_PROXY_ADDRESS:-10.249.250.254}/32
+
 services:
   proxy:
     image: caddy:2.11.4-alpine@sha256:6aeddd44c3078b0f9a35206472a11420648a79c184603ef95957d0a20044cb2b
@@ -59,12 +66,12 @@ services:
   api:
     networks:
       edge: {}
-    environment:
-      # Exactly one trusted peer: this proxy. Set here from the same variable that fixes the proxy's
-      # address, so the two cannot drift apart. These override any value in ekklesia.env.
-      EKKLESIA_CLIENT_ADDRESS_MODE: trusted-proxy
-      EKKLESIA_CLIENT_ADDRESS_HEADER: x-forwarded-for
-      EKKLESIA_CLIENT_ADDRESS_TRUSTED_PROXIES: ${EKKLESIA_PROXY_ADDRESS:-10.249.250.254}/32
+    environment: *ekklesia-client-address
+
+  # Operator commands (migrations, Doctor) run as `migrate`. It gets the API's client-address
+  # configuration too, so that Doctor checks what the API actually runs rather than an empty one.
+  migrate:
+    environment: *ekklesia-client-address
 
   object-storage:
     networks: