fix(scriberr): force uv to copy rather than reflink when building envs

Scriberr builds each model backend's Python environment with uv at
container start. uv's default link mode reflinks or hardlinks out of
its cache, which fails on this overlayfs over ZFS combination and
reports it as a failure to clone a metadata file with errno 11,
resource temporarily unavailable. The wording points nowhere near the
cause.

The damage was partial and therefore easy to miss: WhisperX and
PyAnnote came up fine and the application served normally, while the
Parakeet and Sortformer backends were quietly absent. Setting
UV_LINK_MODE to copy trades a little disk and build time for
environments that actually materialise, and the occurrence count for
that error is zero on the following start.

The knob is exposed through the environment so it can be moved back to
the default if a future host does support reflinks.

stacks/scriberr/compose.yaml

@@ -63,6 +63,13 @@ services:
       # reached by host IP. Keep this in sync with how the app is reached.
       - ALLOWED_ORIGINS=${SCRIBERR_ALLOWED_ORIGINS}
       - NVIDIA_DRIVER_CAPABILITIES=compute,utility
+      # Scriberr builds each model backend's Python env with `uv` at runtime.
+      # uv's default link mode reflink/hardlinks out of its cache, which fails
+      # on this overlayfs+ZFS combination with a misleading
+      #   "Failed to clone ... Resource temporarily unavailable (os error 11)"
+      # and takes out the Parakeet + Sortformer backends (WhisperX survives).
+      # `copy` trades a little disk and time for it actually working.
+      - UV_LINK_MODE=${SCRIBERR_UV_LINK_MODE:-copy}
     deploy:
       resources:
         reservations: