ci: tweak files-changed, add free-disk-space (#37819)

Reduces CI minutes consumption by narrowing the `files-changed` filters.

- DB matrix (`pgsql`/`mysql`/`mssql`/`unit`) now runs only on real
backend changes. `test-sqlite` stays gated on `actions`, so it remains
the smoke check that validates CI-infra changes (composite-action edits,
workflow edits, renovate action-pin bumps) without spinning up the full
matrix.
- Fix the `templates` filter: the SVG template linter is
`tools/lint-templates-svg.ts`, so the `tools/lint-templates-*.js` glob
matched nothing.
- Add missed paths: `tsconfig.json` and
`tools/generate-svg-vscode-extensions.json` to `frontend`,
`eslint.json.config.ts` to `json`, and
`.github/actions/docker-dryrun/**` to `docker`.

---
This PR was written with the help of Claude Opus 4.7

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

.github/actions/go-setup/action.yml

@@ -12,6 +12,7 @@ inputs:
 runs:
   using: composite
   steps:
+    - uses: ./.github/actions/free-disk-space
     - uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0
       with:
         go-version-file: go.mod