Let translators add and remove glossary forms in the localization workspace

[amyjko]

Follow-up from #1241, which added forms to each glossary term — the plurals, conjugations, and synonyms a @reference to that term may use, so an inflected occurrence can be one whole link (@parameters).

Each locale writes its own forms, and how many a language needs is its own business (Hindi needs case-inflected forms English doesn't). But the /localize workspace can't create one today:

• An array-valued string renders as a prev/next walk over the elements that already exist (/localize/+page.svelte, moveTupleIndex, clamped to the saved value's length). There is no add- or remove-element affordance anywhere in the editor.
• The server-side applier refuses to grow an array: submitLocalization.ts throws on an index outside the saved bounds.

So a locale's first adoption of forms is a hand edit to its JSON plus a pull request — the same starting point guidance had before it got a dedicated editor.

Worth deciding whether this is a general "editable string list" affordance (it would also serve input.Key.keys synonym lists and names aliases) or something specific to glossary forms, presented next to the term's word and definition.