[FEAT] Add CLDR plural form support to localization system

[PawiX25]

Problem

The current localization system (FlowLocalizations) uses simple string interpolation with {count} or {} placeholders for numeric values. This doesn't support grammatical plural forms, which differ across languages.

For example, the key tabs.home.transactionsCount with value "{count} transactions" always shows the same noun form regardless of the count:

• English: "1 transactions" ❌ (should be "1 transaction")
• Polish: "1 transakcji" ❌ (should be "1 transakcja", and "2 transakcje" for few)
• Russian: "1 транзакций" ❌ (should be "1 транзакция", and "2 транзакции" for few)

This affects all 14 supported languages — some have simple singular/plural (English, German), while others have complex plural rules (Polish, Russian, Czech, Arabic).

Proposed Solution

Add CLDR-based plural category resolution to FlowLocalizations.getTransalation():

1. New static method _pluralCategory(num n, String langCode) that returns the appropriate CLDR plural category (one, few, many, two, zero, other) based on the language and count value.

2. Modified num handling in getTransalation(): When replace is a num, the system checks for a suffixed key (e.g., key.one, key.few, key.many) before falling back to the base key.

3. Plural form keys in l10n JSON files: Languages can optionally define suffixed keys for each plural form. If a suffixed key doesn't exist, the base key is used (fully backward-compatible).

CLDR Rules Coverage (all 14 Flow languages)

Language	Code	Categories	Rule
Polish	pl	one/few/many	one (1), few (2-4 excl. 12-14), many (rest)
Russian	ru	one/few/many	one (%10=1, %100≠11), few (%10=2-4, %100≠12-14), many
Ukrainian	uk	one/few/many	same as Russian
Belarusian	be	one/few/many	same as Russian
Czech	cs	one/few/other	one (1), few (2-4), other
Arabic	ar	zero/one/two/few/many/other	full CLDR Arabic rules
French	fr	one/other	one (0-1), other
Persian	fa	one/other	one (0-1), other
English	en	one/other	one (1), other
German	de	one/other	one (1), other
Italian	it	one/other	one (1), other
Spanish	es	one/other	one (1), other
Turkish	tr	one/other	one (1), other
Mongolian	mn	one/other	one (1), other

Example JSON (Polish)

"tabs.home.transactionsCount": "{count} transakcji",
"tabs.home.transactionsCount.one": "{count} transakcja",
"tabs.home.transactionsCount.few": "{count} transakcje",
"tabs.home.transactionsCount.many": "{count} transakcji"

Backward Compatibility

• If no suffixed keys exist for a language, the base key is used as before
• No changes needed in calling code — the .t(context, count) API is unchanged
• Languages can incrementally add plural forms for any key