Preserve query parameters in form options sources

[lovasoa]

Motivation

• The existing options loader built the remote options URL by string-concatenation and appended ?search=..., which dropped or corrupted any existing query parameters in options_source URLs.
• This broke use-cases where options_source already contained parameters (for example ...?id=... or ?category=...) and required a robust way to add/replace the search parameter.

Description

• In sqlpage/tomselect.js replaced string concatenation with the browser URL API and URLSearchParams to build the request URL: new URL(options_source, document.baseURI) and options_url.searchParams.set("search", query) before calling fetch.
• Updated the end-to-end test tests/end-to-end/official-site.spec.ts to exercise and assert that existing query parameters are preserved when remote searches run.
• Documented the behavior and example options_source with an existing query parameter in examples/official-site/sqlpage/migrations/01_documentation.sql.
• Added a brief CHANGELOG.md entry describing the fix.

Testing

• Ran npm run format which completed successfully.
• Ran npm test (the repository biome check step) which completed successfully but reported lint diagnostics/warnings (no test failures).
• Ran git diff --check which reported no issues after the changes.

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Codex Task