Fix stale UI cache, BEN2 edge quality, and fresh-install permissions

- Serve /dist and /src with Cache-Control: no-cache so browsers always
  revalidate the webpack bundle (it has a fixed filename with no content
  hash, so a stale browser cache was hiding the new Remove Background
  model dropdown after the rebuild).
- Enable BEN2's refine_foreground pass by default - it's the model's own
  documented option for preserving fine/semi-transparent edge detail
  (text borders, light rays) instead of a harder cutout, at a small
  speed cost.
- Make install-local-gpu.sh and bring-up-local-gpu.sh pre-create ./data
  as the invoking non-root user before Docker ever runs, so its daemon
  never gets a chance to auto-create those bind-mount dirs as root.
- Make prefetch-models.sh self-heal a root-owned ./data automatically
  (sudo chown) instead of erroring out with a manual fix-it command.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ro4PwQKvSc3CH19LSN21Ht

bring-up-local-gpu.sh

@@ -19,6 +19,15 @@
 
 set -euo pipefail
 
+cd "$(dirname "$0")"
+
+# Pre-create ./data as the current (non-root) user. Otherwise, on a fresh
+# checkout, Docker's daemon (root) auto-creates these bind-mount sources on
+# the first 'up' — leaving them root-owned and blocking this same user from
+# later writing to them without sudo (e.g. ./prefetch-models.sh). No-op if
+# they already exist, regardless of current ownership.
+mkdir -p data/models data/hf_cache data/projects data/patches
+
 if [ $# -eq 0 ]; then
     exec docker compose -f docker-compose.gpu.yml up -d --build
 else