fix: release QA hardening across processing, media, security, and CI gates (#649)

A release-readiness QA pass over the whole product. The commits split into
defects a user would hit and gates that were reporting green while measuring
nothing.

## Fixes that change behaviour

Rate limiting was bypassable on every install: TRUST_PROXY defaulted to true, so
request.ip came from a client-set header and a forged X-Forwarded-For got past
the login limiter. The default is now a private-network trust list.

A transient Postgres outage stranded in-flight jobs, leaving finished output on
disk with no row pointing at it. A reconciler now resolves those rows and adopts
the bytes rather than dropping the work.

A Redis connection that moved to a new address wedged every read-blocked
consumer, so completions stopped signalling while health still answered 200.
Socket timeouts plus subscriber pings recover it.

Installing more than one AI bundle left the shared venv multi-versioned and
silently broke three tools. The installer now reconciles distributions to one
version each.

Converting an image to JXL at quality 1 through 4 returned a 500, because
libjxl 0.7 rejects the distance those values compute. The quality is floored at
what the encoder honours. A missing ffmpeg was also reported to the user as a
corrupt upload; it now says the engine is unavailable.

RAW uploads reached an unpatched LibRaw on arm64, so it is built from source at
0.22.2, and the release scan was split so it can fail on an unfixed critical
instead of hiding it behind ignore-unfixed.

## Gates that could not fail

Two mutation lanes ran zero mutants because Stryker crawled the gitignored docs
build; coverage discarded its whole report on any failing test; the lint gate
skipped root tests, scripts, and two workspaces; and several generated matrices
counted a host missing ffmpeg as a passing tool. Each now measures what it
claims.

Full evidence and the outstanding release items are tracked locally and are not
part of this branch.

docker/docker-compose-gpu.yml

@@ -38,7 +38,9 @@ services:
       - RATE_LIMIT_PER_MIN=${RATE_LIMIT_PER_MIN:-1000}
       - MAX_USERS=${MAX_USERS:-0}
       - SESSION_DURATION_HOURS=${SESSION_DURATION_HOURS:-168}
-      - TRUST_PROXY=${TRUST_PROXY:-true}
+      # Believe X-Forwarded-For only from a peer on a private network. Set to
+      # `true` only if a proxy you control sits in front on a public address.
+      - TRUST_PROXY=${TRUST_PROXY:-loopback,linklocal,uniquelocal}
       - DATABASE_URL=postgres://${POSTGRES_USER:-snapotter}:${POSTGRES_PASSWORD:-snapotter}@postgres:5432/${POSTGRES_DB:-snapotter}
       - REDIS_URL=redis://:${REDIS_PASSWORD:-snapotter}@redis:6379
       # 1.x upgrade: uncomment to import the old SQLite database on first boot;
@@ -91,9 +93,10 @@ services:
       # signal a different-UID process, so docker stop is ungraceful
       # ("[FATAL tini] forwarding signal: Operation not permitted" -> SIGKILL).
       - KILL
-    # NOTE: security_opt: [no-new-privileges:true] is intentionally omitted.
-    # gosu requires setuid to drop from root to the snapotter user.
-    # Mitigation: cap_drop: ALL limits available capabilities after privilege drop.
+    # The entrypoint can still drop from root to the snapotter user while this
+    # prevents setuid binaries from granting privileges to untrusted processes.
+    security_opt:
+      - no-new-privileges:true
     # NOTE: read_only: true is not set because PUID/PGID remapping requires
     # writing to /etc/passwd and /etc/group. Consider using Docker --user flag
     # instead of PUID/PGID for read-only rootfs support.
@@ -118,7 +121,7 @@ services:
         max-file: "5"
 
   postgres:
-    image: postgres:17-alpine
+    image: postgres:17-alpine@sha256:742f40ea20b9ff2ff31db5458d127452988a2164df9e17441e191f3b72252193
     container_name: SnapOtter-postgres
     environment:
       POSTGRES_USER: ${POSTGRES_USER:-snapotter}
@@ -134,8 +137,8 @@ services:
     cpus: 2
     pids_limit: 256
     # The official image starts as root and su-execs down to the postgres user,
-    # so setuid/setgid + chown caps are required. no-new-privileges and a
-    # read-only rootfs are omitted for the same privilege-drop reason as the app.
+    # so setuid/setgid + chown caps are required. A read-only rootfs is omitted
+    # because the entrypoint must initialize and adjust its data directory.
     cap_drop:
       - ALL
     cap_add:
@@ -144,6 +147,8 @@ services:
       - FOWNER
       - SETGID
       - SETUID
+    security_opt:
+      - no-new-privileges:true
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-snapotter} -d ${POSTGRES_DB:-snapotter}"]
       interval: 10s
@@ -152,7 +157,7 @@ services:
       start_period: 15s
 
   redis:
-    image: redis:8-alpine
+    image: redis:8-alpine@sha256:9d317178eceac8454a2284a9e6df2466b93c745529947f0cd42a0fa9609d7005
     container_name: SnapOtter-redis
     command: >-
       redis-server
@@ -169,8 +174,8 @@ services:
     cpus: 2
     pids_limit: 256
     # The official image starts as root and gosu-drops to the redis user, so
-    # setuid/setgid + chown caps are required; no-new-privileges and a read-only
-    # rootfs are omitted for the same privilege-drop reason as the app.
+    # setuid/setgid + chown caps are required. A read-only rootfs is omitted
+    # because the entrypoint must initialize and adjust its data directory.
     cap_drop:
       - ALL
     cap_add:
@@ -179,6 +184,8 @@ services:
       - FOWNER
       - SETGID
       - SETUID
+    security_opt:
+      - no-new-privileges:true
     healthcheck:
       test: ["CMD", "redis-cli", "-a", "${REDIS_PASSWORD:-snapotter}", "--no-auth-warning", "ping"]
       interval: 10s