Remove the orphaned Qt-era island bundles from assets/

[dovvnloading]

Problem

Under the Qt architecture, each webview hosted its own fully self-contained Vite bundle under assets/<island>/, which graphlink_composer_web.py's _inline_bundle() inlined into a single offline HTML document.

R7.6a replaced all 19 islands with the SPA and deleted their source (web_ui/src/islands/), the 19-entry build registry in vite.config.ts, and that consumer module — but the compiled output stayed committed. vite.config.ts still records what happened:

"This config used to carry a 19-entry ISLANDS registry and a GRAPHLINK_ISLAND env switch… R7.6a deleted every island — the SPA replaced all 19 — so the switch, the registry, and the per-island outDir have nothing left to select between."

Change

Deletes the 19 leftover bundle directories, plus four static files orphaned by the same migration: the two Qt stylesheet images (down_arrow.png for combobox arrows, check.png for checkbox indicators), File.png, and the Qt splash audio.

.gitattributes drops its web_ui/src/islands/*/index.html rule, whose path no longer exists. The assets/*/** rule is kept with its behaviour unchanged and its comment corrected — it now covers the surviving assets/branding/ and assets/screenshots/ rather than island build output.

Untouched: assets/graphlink.ico (used by graphlink_desktop.py and tools/build_app_icon.py) and assets/branding/ (used by build_app_icon.py and gl-vars-dev.css).

This is repo-only weight — pyproject.toml packages only backend* and graphlink_plugins*, so none of it shipped in the wheel.

Evidence it was dead

Check	Result
Code references to any of the 19	None — only a .gitattributes rule and two gitignored /doc/ planning files
Backend serves them?	No — app.mount("/assets", …) points at web_ui/dist/app/assets, not the repo root
Any build regenerates them?	No — the SPA under src/app is the only build target
Consumer module	graphlink_composer_web.py deleted
Live PySide6 imports	Zero
Tracked references to the four static files	Zero

Test plan

• Full backend suite: 3020 passed, 17 skipped
• Full frontend check: 1944 tests, zero lint errors, build and bundle size clean
• ruff clean
• graphlink_desktop.py's icon path still resolves; tools/build_app_icon.py still runs
• Every remaining .gitattributes rule verified to still match real tracked files (20 / 26 / 1)