refactor(sonar): use non-deprecated ThemeProvider (typescript:S1874)

[setchy]

SonarCloud: typescript:S1874 (filtered issues)

Resolves Sonar rule typescript:S1874 — Deprecated APIs should not be used (partial).

Moved ThemeProvider from @primer/react to @primer/react/next (the documented non-deprecated replacement), clearing 3 of 5 issues.

Remaining: TextInputWithTokens (2 issues) — accepted; path agreed (option A).

In Primer v38.40 there is no non-deprecated multi-token input. Autocomplete is single-select and is not a viable replacement. Primer's own guidance (primer/react#6713) is to keep the component and import it from the deprecated entrypoint:

import { TextInputWithTokens } from '@primer/react/deprecated';

That entrypoint ships the component in a future version (v39 is in RC; latest stable is 38.40.1). Existing residents of @primer/react/deprecated (e.g. Pagehead) do not carry the @deprecated JSDoc tag, so this one-line import relocation is expected to clear both remaining S1874 findings with zero UX change.

Plan: when renovate bumps @primer/react to v39, relocate the import (one line). A custom token input built on TextInput + Token primitives is the long-term alternative, intentionally out of scope here.

Lint, tsc, and the full test suite pass.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[setchy]

Superseded by #3394, which includes the same ThemeProvider migration plus aligned hook/type imports, mock and visual-harness updates, and 29 real-provider integration tests. Closing this draft as superseded, not as merged or as confirmation that the SonarCloud findings are resolved; #3394 still needs its CI and SonarCloud results confirmed.

Preserving the follow-up recorded in this PR: revisit TextInputWithTokens when Renovate upgrades @primer/react to v39, check whether @primer/react/deprecated exports it and whether relocating the import actually clears the remaining S1874 findings, and retain the existing UX. That token-input work is not included in #3394 and remains a separate follow-up.