Qt-removal R7.6a: delete the island half

[dovvnloading]

First of three cutover sub-increments. Removes the 19 pre-SPA island frontends and everything that existed only to serve them. graphlink_app/ stays in place for R7.6b.

Change

• Deletes web_ui/src/islands/ (19 islands, 429 island tests).
• Simplifies vite.config.ts to a single build target — the GRAPHLINK_ISLAND switch, the 19-entry ISLANDS registry, and the per-island outDir had nothing left to select between. npm run dev no longer needs an env var.
• Removes the three tests that read island source files (details below).

The codegen registry is deliberately left whole at 25 entries. An earlier revision of this PR pruned it to the 11 the SPA imports, which broke CI. The payload dataclasses that feed the codegen still live in graphlink_app/, and the repo deliberately couples them: every payload has a committed generated artifact plus a staleness test asserting they match, and the codegen CLI's own drift tests use a generated file as their fixture. Pruning one side of that pair violated an invariant the repo enforces on purpose — 61 tests said so. The prune belongs in R7.6b, where the dataclasses, the codegen, and their tests are deleted together as the one unit they actually are. Cost: 28 unimported generated files survive one more increment.

Removed tests, and what each costs

• test_composer_token_retrofit.py + its pre-retrofit fixture. The whole file is coverage for islands/composer/styles.css. Its 7 still-passing tests only assert internal consistency of --gl-composer-* tokens, which now have no consumer. This does drop the guard keeping those tokens out of the Tailwind theme block for one increment; graphlink_styles.py and the tokens themselves go in R7.6b.
• test_gl_vars_dev_css.py::test_it_is_imported_behind_the_dev_flag — asserted islands/composer/main.tsx guards the import behind import.meta.env.DEV. The sibling whole-tree scan (which carries an explicit SPA carve-out) still passes and is the guard with actual teeth.
• test_composer_model_controls.py::test_composer_footer_has_stable_model_width_and_no_status_dot — a pure island CSS/TSX assertion.

Coupled fix

no-raw-colors.test.ts scanned islands/**, which no longer exists. It now scans app/**, bringing the SPA under the design-token guard for the first time. That surfaced 8 pre-existing literals in app/styles.css, pinned rather than excluded — same idiom as qt_burndown.json, so the count can only go down and any new literal fails the build.

They are not swapped for tokens here because none is a like-for-like substitution: --gl-shadow-3 is 0 8px 28px rgba(0,0,0,0.55), which shares geometry with one offender and alpha with another but equals neither; rgba(0,0,0,0.43) is a scrim with no token; and var(--gl-accent, #6ea8fe)'s fallback is load-bearing because --gl-accent isn't defined in the generated token files. Doing it correctly changes rendered output and belongs in a design pass, not an island deletion.

Test plan

• python -m pytest -q (what CI runs, whole repo): 2505 passed
• npm run check: 779 frontend tests, 0 lint errors, typecheck/build clean
• check:schema passes against the intact 25-entry registry
• Burn-down gate unchanged at 152/84/68 — no Qt file was touched, by design