feat: sync current slide with a URL query parameter

[HeikoGr]

What

New option urlHash (default false). When enabled:

• On start, the carousel jumps to the slide given in the URL hash, e.g. http://localhost:8080/#3.
• Changing the hash while the page is open (link, bookmark, address bar) navigates as well.
• A number selects the slide 1-indexed, the same as CAROUSEL_GOTO. In slides mode, a slide name works too, e.g. #Home.
• Every slide change writes the current slide number back to the hash, so the address bar always shows a link to the visible page.

Why

Many setups show the mirror in a browser (tablet, second screen, serveronly). A URL per page makes it possible to bookmark a page, share a link to it, or have a kiosk browser start on a given page. Before this change, there was no way to do that without a remote-control module.

How

• Hash parsing (decodeUrlHash, parseUrlHash) returns the same payloads that handleCarouselGoto accepts. Navigation therefore goes through the existing CAROUSEL_GOTO path, including restartTimer, so transitionTimeout and homeSlide behave the same as with any other manual navigation.
• moduleTransition calls updateUrlHash, which uses history.replaceState. This does not fire hashchange, so there is no feedback loop, and automatic rotation does not add browser history entries.
• updateUrlHash is inactive until setupUrlHash has run. Without that guard, the initial transition would overwrite the start hash with #1 before it was read.
• Unknown slide names log a warning and are ignored.
• positional mode is not supported, because each position has its own index. A warning is logged, the same as for enableKeyboardControl.

Tests

• New unit tests for parseUrlHash, setupUrlHash and updateUrlHash. The window mock in the test context is now a named object so tests can stub location, history and addEventListener.
• node --run test passes: unit tests, eslint, prettier and cspell.
• Tested manually in headless Chrome with slides mode and MMM-KeyBindings 3.1.0:
  • start with #2
  • hash change to a name and to a number
  • arrow key and next button update the hash
  • an unknown name is ignored with a warning

🤖 Generated with Claude Code

[KristjanESPERANTO]

Thanks for the PR! This seems like a useful feature. What do you think of a namespaced query parameter such as ?carousel=3 or ?carousel=Home instead of the raw URL hash? The hash is shared with page anchors and other modules, while URLSearchParams would avoid collisions.

[HeikoGr]

you are right about the namespace. ?carousel=n would be fine.

[KristjanESPERANTO]

Nice. Would you like to adapt your PR? :)

[HeikoGr]

@KristjanESPERANTO yes. i let claude rework the patch

[KristjanESPERANTO]

Thanks :) I saw your commit. I'll need a little time to review it.

[KristjanESPERANTO]

I did some more fine-tuning and included it in the new release 😃 Thanks again!