Manager UI - Delete 12 dead .less stylesheets

[agalin920]

Closes #4300

Phase 1 of #4265, the .less retirement. Deletes the 12 stylesheets that cannot affect anything that renders — 269 lines, no insertions — taking src/ from 82 .less files to 70 and from 3,110 LOC to 2,842. Eleven of them are referenced from nothing anywhere in the repo, verified by grepping each basename across the whole tree rather than just src/, and there is no dynamic route by which they could still be pulled in: require.context appears nowhere, no glob or template-literal stylesheet import exists, and .less is absent from resolve.extensions (src/shell/webpack.config.js:106) so a bare import "./Content" cannot resolve to Content.less.

The twelfth needs its own sentence, because it is the only one that was imported. src/shell/webpack.config.js:263-278 runs every .less through css-loader with modules: { localIdentName: "[local]--[contenthash:base64:5]" } — unconditionally; the dev/prod ternary above that rule wraps only the ts-loader/babel-loader entry. So .FieldTypeUUID is emitted as FieldTypeUUID--<hash>, obtainable only from the imported styles binding. FieldTypeUUID.js never dereferences that binding, sets no className at all, and spreads no props — it names required, value, name, datatype and onChange individually, so a parent cannot inject a class through it either, and its sx targets the MUI global .MuiInputBase-readOnly rather than a module class. Nothing else in the repo imports the file or hardcodes the class. Those rules therefore already apply to no element on dev today; deleting them changes no rendered pixel. Restoring that styling would be a new design ask, not a regression from this PR. The now-dangling import styles line goes with it, along with the import cx from "classnames" beside it, which is unused for the same reason.

No colour or token work is included, so this phase is independent of #4264. Both npm run build:dev and npm run build:stage compile the branch with zero errors — the latter cacheless by construction, since webpack's filesystem cache is enabled only when NODE_ENV === "development" — which is the check that matters here: a resolving build is the only way to prove no importer was left dangling. tsc --noEmit reports no errors.

[github-actions]

Coverage Report

Overall Coverage

Lines	Statements	Branches	Functions
61.34%	60.90%	56.20%	55.70%

Changed Files Coverage

File	Lines	Statements	Branches	Functions
src/shell/components/FieldTypeUUID/FieldTypeUUID.js	53.84%	53.84%	87.50%	28.57%