feat: api client support for triggering builds

[Scr4tch587]

What

Adds triggerBuild() and dryRunBuild() to the typed api client (lib/api.ts), both hitting POST /api/v1/build/{name}/{version} — the dry-run variant passes dry-run=true. Adds the BuildResponse and DryRunBuildResponse types (dry-run reuses the existing DataRow shape, same as GET /data).

Why

The browsing UI is deliberately read-only (build-data=false everywhere), so until now the only way to build data was curl. This gives the frontend a typed path to the existing build endpoint ahead of the build-panel UI (next PR in the stack).

Benefit

Builds become explicitly triggerable from the browser, with dry runs available to preview builder output without writing to the db. Errors reuse ApiError, so backend detail messages (e.g. 422 no-valid-timestamps) surface verbatim in the UI.

[github-actions]

• main
  • feat: replace svelte frontend with react + tailwind scaffold #375
    • feat: typed api client and api key handling #376
      • feat: dataset browsing ui #377
        • ci: deploy frontend to github pages #378
          • docs: update specs for react migration #379
            • feat: github rest client for dataset proposals #383
              • feat: dataset proposal service and endpoint #384
                • feat: api client support for dataset proposals #385
                  • feat: dataset creation ui #386
                  • docs: document dataset proposal flow in specs #387
                  • feat: api client support for triggering builds 👈
                  • feat: build trigger ui #389
                  • docs: document build trigger in frontend spec #390