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.

packages/ai/python/offline_guard.py

@@ -1,37 +1,31 @@
-"""Gate for runtime model downloads, with an optional strict offline mode.
+"""Gate runtime model downloads behind an explicit opt-in.
 
 Models normally arrive through user-initiated feature bundle installs
 (install_feature.py), and the resolvers in the AI scripts always prefer those
-bundled files. When a model is missing, scripts may fetch the public model
-weights as a fallback so tools work out of the box; that fallback only ever
-downloads public model files, never user data.
-
-Setting SNAPOTTER_ALLOW_MODEL_DOWNLOAD=0 enables strict offline mode for
-airgapped or locked-down deployments: every script calls
-ensure_download_allowed() immediately before any download fallback, so a
-missing file then surfaces as an actionable error instead of an outbound
-fetch.
+bundled files. If a model is missing, the runtime fails closed instead of
+fetching mutable content. Operators may explicitly opt into public model
+fallback downloads with SNAPOTTER_ALLOW_MODEL_DOWNLOAD=1.
 """
 import os
 
 
 def downloads_allowed():
-    """True unless strict offline mode is explicitly enabled.
+    """Return True only when runtime downloads are explicitly enabled.
 
-    Runtime model downloads are allowed by default; only an explicit
-    SNAPOTTER_ALLOW_MODEL_DOWNLOAD=0 (or "false") blocks them.
+    Unknown values remain fail-closed to avoid enabling network access through
+    a typo or an inherited environment setting.
     """
-    return os.environ.get("SNAPOTTER_ALLOW_MODEL_DOWNLOAD", "1").lower() not in ("0", "false")
+    return os.environ.get("SNAPOTTER_ALLOW_MODEL_DOWNLOAD", "0").lower() in ("1", "true")
 
 
 def ensure_download_allowed(what):
-    """Raise a clear, actionable error when strict offline mode blocks a fetch."""
+    """Raise a clear, actionable error when runtime downloads are disabled."""
     if downloads_allowed():
         return
     raise RuntimeError(
-        f"{what} is missing and automatic downloads are disabled by "
-        "SNAPOTTER_ALLOW_MODEL_DOWNLOAD=0. Reinstall the feature bundle from "
-        "Settings, or unset SNAPOTTER_ALLOW_MODEL_DOWNLOAD to permit downloads."
+        f"{what} is missing and automatic downloads are disabled. Reinstall "
+        "the feature bundle from Settings, or explicitly set "
+        "SNAPOTTER_ALLOW_MODEL_DOWNLOAD=1 to permit runtime downloads."
     )