fix(ui): map drop-style page URLs to markdown twins

[ngarakapati]

Summary

Copy page / View as Markdown / Open in ChatGPT·Claude·Cursor all look up a .md twin by swapping .html → .md.

Production docs omit .html (/savanna/main/overview/), so the button currently gets data-md-url="./" and fetches the HTML page.

This updates md-url so both URL styles work:

• /overview/index.html → /overview/index.md
• /overview/ → /overview/index.md
• /overview/pricing → /overview/pricing.md

build/ui-bundle.zip is rebuilt with the helper.

Merge order

Merge this PR first, then the companion change on cloud-docs#171 (htmlToMdUrl in lib/llm-utils.js) so the published .md paths match what the button fetches.

Based on current main after #47, so no rebase conflict with that merge.

[Tushar-TG-14]

@ngarakapati
Could we add unit tests for md-url.js covering the three URL styles mentioned in the PR description, along with query strings/hash fragments? Since this helper is now used by Copy page / View as Markdown / ChatGPT / Claude / Cursor, having explicit tests would help prevent regressions in URL generation.

Can we confirm that query parameters and hash fragments are preserved correctly for the new URL styles? For example, /overview/?foo=bar should resolve to /overview/index.md?foo=bar, and /overview/index.html#section to /overview/index.md#section. A unit test for these cases would make this explicit.

Has the rebuilt build/ui-bundle.zip been generated from the exact final version of src/helpers/md-url.js, and has the updated bundle been tested in the Cloud/Savanna preview?

[ngarakapati]

Added unit tests for md-url.js (npm test / node test/helpers/md-url-test.js). They cover the three URL styles from the PR, plus query strings and hashes, including:

• /overview/?foo=bar → /overview/index.md?foo=bar
• /overview/index.html#section → /overview/index.md#section
• /overview/index.html?foo=bar#section → /overview/index.md?foo=bar#section

Query and hash are preserved on all three styles. 15 cases, all passing.

Rebuilt build/ui-bundle.zip from this same src/helpers/md-url.js. Unzipping the helper out of the zip matches the source file. I also ran the packed helper through the page-actions template the way Antora would: Savanna drop-style URLs get data-md-url="index.md", and ?foo=bar / #section stay on that URL.