perf(ui): delegate BxSelect option re-rendering to a single global observer

[Endymi0n74]

What

Every BxSelectElement.create() was attaching its own MutationObserver to the <select> (subtree + childList + attributes). With many selects in the settings dialogs that's one observer per select, all watching the same document.

Now a single static observer watches document.documentElement once and routes mutations to the affected .bx-select wrappers via closest(), only re-rendering selects whose own subtree actually changed (deduplicated with a Set per mutation batch). All other re-render triggers (input, change, value setter) are unchanged.

Also removes a leftover debugger; statement in Translations.downloadTranslations()'s catch block — a no-op in production except pausing the script when the DevTools are open.

Why it's safe

• Same events observed (childList + subtree + attributes) — just on one shared observer instead of N.
• Routing via closest('.bx-select') targets the same wrappers; the per-select re-render logic is untouched.
• The Set dedup prevents double re-renders within a mutation batch (strictly fewer renders than before).

Files

• src/web-components/bx-select.ts — static global observer + ensureObserver() + delegated onMutation
• src/utils/translation.ts — debugger; removed from the catch block

Note

translation.ts is also touched by the open PRs #908 (mkb zoom), #938 (local co-op) and #468 (record) — all in different regions (the debugger line is ours). Happy to rebase if any of them merges first.