Add VAPID config and the push subscription API

Require MEALQUEST_VAPID_PUBLIC_KEY, MEALQUEST_VAPID_PRIVATE_KEY_FILE and
MEALQUEST_VAPID_SUBJECT at boot. Both keys are unpadded base64url P-256
keys, the encoding webpush-go reads; boot derives the public point from the
private key and refuses a pair that does not match. The subject must be
mailto:<address> or an https:// URL.

internal/push stores subscriptions by endpoint: GET
/api/v1/push/vapid-public-key serves only the public key, POST
/api/v1/push/subscriptions upserts {endpoint, keys.p256dh, keys.auth,
user_agent}, and DELETE removes by endpoint, answering 204 whether or not
it was stored. cmd/vapidgen prints a new key pair. deploy/compose.yaml
mounts the vapid_private_key secret.

Maestro task e8a7b1f4-327a-478b-88c7-5d265afda153.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

deploy/.env.example

@@ -6,7 +6,8 @@
 #
 # Secrets are never set here. They live in deploy/secrets/ (never committed),
 # one value per file, owned by the container user 10001:10001 with mode
-# 0600: secret_key, oidc_client_secret and google_client_secret. SearXNG's
+# 0600: secret_key, oidc_client_secret, google_client_secret and
+# vapid_private_key. SearXNG's
 # searxng.env is the exception: compose reads it itself, so it is owned by
 # the host account that runs compose, mode 0600. Creating them: CTXD project
 # mealquest, RUNBOOKS.MD "Stack and first deploy" > "4. Secrets".
@@ -57,6 +58,19 @@ MEALQUEST_OIDC_ALLOWED_GROUPS=mealquest-admin
 # URI is <MEALQUEST_PUBLIC_URL origin>/api/v1/integrations/google/callback.
 MEALQUEST_GOOGLE_CLIENT_ID=<client id>.apps.googleusercontent.com
 
+# --- Web Push (VAPID) ------------------------------------------------------
+
+# Required: the service will not start without the public key, the subject
+# and the private key file, or with a private key that does not belong to
+# the public key. `go run ./cmd/vapidgen` prints a new pair: its
+# MEALQUEST_VAPID_PUBLIC_KEY line goes here, its private key line alone
+# into deploy/secrets/vapid_private_key. Both are unpadded base64url P-256
+# keys. Key pair: CTXD project mealquest, RUNBOOKS.MD "VAPID keys (Web
+# Push)". Replacing the pair invalidates every browser's subscription.
+MEALQUEST_VAPID_PUBLIC_KEY=<base64url VAPID public key>
+# The push services' contact for this sender: mailto:<address> or https://.
+MEALQUEST_VAPID_SUBJECT=mailto:<owner address>
+
 # Optional session lifetimes. A session ends after IDLE unused and always MAX
 # after sign-in; MAX must be at least IDLE. Defaults: 720h and 4320h.
 MEALQUEST_SESSION_IDLE=720h
@@ -72,18 +86,10 @@ MEALQUEST_SESSION_MAX=4320h
 #   The Authentik provider's client secret.
 # MEALQUEST_GOOGLE_CLIENT_SECRET_FILE=/run/secrets/google_client_secret
 #   The Google OAuth web client's secret.
+# MEALQUEST_VAPID_PRIVATE_KEY_FILE=/run/secrets/vapid_private_key
+#   The VAPID private key printed by `go run ./cmd/vapidgen`.
 # MEALQUEST_SEARXNG_URL=http://searxng:8080
 #   The SearXNG recipe-search sidecar on the compose network. The Settings
 #   screen pre-fills it as the SearXNG URL until one is saved; the saved
 #   provider and base URL come from PATCH /api/v1/settings/recipe-search.
 #   See CTXD project mealquest, RUNBOOKS.MD "Recipe search (SearXNG)".
-
-# --- Planned; not read by the service yet -------------------------------------
-#
-# Added to deploy/compose.yaml and this file by the features that use them.
-#
-# Web Push (Feature 19). Key pair: CTXD project mealquest, RUNBOOKS.MD
-# "VAPID keys (Web Push)".
-# MEALQUEST_VAPID_PUBLIC_KEY=<base64url VAPID public key>
-# MEALQUEST_VAPID_PRIVATE_KEY_FILE=/run/secrets/vapid_private_key
-# MEALQUEST_VAPID_SUBJECT=mailto:<owner address>

deploy/compose.yaml

@@ -31,11 +31,13 @@ services:
       MEALQUEST_SECRET_KEY_FILE: /run/secrets/secret_key
       MEALQUEST_OIDC_CLIENT_SECRET_FILE: /run/secrets/oidc_client_secret
       MEALQUEST_GOOGLE_CLIENT_SECRET_FILE: /run/secrets/google_client_secret
+      MEALQUEST_VAPID_PRIVATE_KEY_FILE: /run/secrets/vapid_private_key
       MEALQUEST_SEARXNG_URL: http://searxng:8080
     secrets:
       - secret_key
       - oidc_client_secret
       - google_client_secret
+      - vapid_private_key
     volumes:
       - mealquest-data:/data
     ports:
@@ -130,6 +132,8 @@ secrets:
     file: ./secrets/oidc_client_secret
   google_client_secret:
     file: ./secrets/google_client_secret
+  vapid_private_key:
+    file: ./secrets/vapid_private_key
 
 volumes:
   mealquest-data: