Update WebGPU bridge assets to v0.1.14

[leehack]

Summary

• bump the default WebGPU bridge asset tag to v0.1.14
• document the BERT embedding pthread-pool sizing fix from BERT embedding silently aborts on web llama-web-bridge#5
• keep the llama.cpp revision aligned at b9016

Verification

• bash -n scripts/fetch_webgpu_bridge_assets.sh
• WEBGPU_BRIDGE_ASSETS_TAG=v0.1.14 ./scripts/fetch_webgpu_bridge_assets.sh
• dart test -p chrome test/unit/backends/webgpu/interop_test.dart test/unit/backends/webgpu/webgpu_backend_test.dart
• dart analyze

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.72%. Comparing base (e9d9908) to head (a59b0b2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #118   +/-   ##
=======================================
  Coverage   76.72%   76.72%           
=======================================
  Files          70       70           
  Lines        8732     8732           
=======================================
  Hits         6700     6700           
  Misses       2032     2032           

Flag	Coverage Δ
unittests	76.72% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.