feat: add Italian language translation support (#11844)

### What problem does this PR solve?

- Add complete Italian translation file with all UI sections
- Register Italian in LanguageAbbreviation enum and language maps
- Configure Italian translation in i18n config
- Add Italiano to language selector dropdown


### Type of change

- [x] Other (please describe):

## What
Added complete Italian language translation support to RAGFlow

## Changes
- Added comprehensive Italian translation file
([it.ts](ragflow/web/src/locales/it.ts:0:0-0:0)) with all UI sections
(1239 lines)
- Registered Italian in `LanguageAbbreviation` enum and all language
maps
- Configured Italian translation in i18n configuration
- Added "Italiano" to language selector dropdown

## Impact
- Italian users can now use RAGFlow in their native language
- All major UI components are translated including:
  - Login/registration screens
  - Knowledge base management
  - Chat interface
  - Settings and configuration
  - Admin console
  - Error messages and notifications

## Testing
- Verified all translation keys are present
- Confirmed language selector shows "Italiano" correctly
- Tested that no translation keys are missing
- All UI sections properly translated

Co-authored-by: PentaFrame <info@pentaframe.it>

web/src/constants/common.ts

@@ -51,6 +51,7 @@ export const LanguageList = [
   'Portuguese BR',
   'German',
   'French',
+  'Italian',
 ];
 export const LanguageMap = {
   English: 'English',
@@ -64,6 +65,7 @@ export const LanguageMap = {
   'Portuguese BR': 'Português BR',
   German: 'German',
   French: 'Français',
+  Italian: 'Italiano',
 };
 
 export enum LanguageAbbreviation {
@@ -78,6 +80,7 @@ export enum LanguageAbbreviation {
   PtBr = 'pt-BR',
   De = 'de',
   Fr = 'fr',
+  It = 'it',
 }
 
 export const LanguageAbbreviationMap = {
@@ -92,6 +95,7 @@ export const LanguageAbbreviationMap = {
   [LanguageAbbreviation.PtBr]: 'Português BR',
   [LanguageAbbreviation.De]: 'Deutsch',
   [LanguageAbbreviation.Fr]: 'Français',
+  [LanguageAbbreviation.It]: 'Italiano',
 };
 
 export const LanguageTranslationMap = {
@@ -106,6 +110,7 @@ export const LanguageTranslationMap = {
   'Portuguese BR': 'pt-br',
   German: 'de',
   French: 'fr',
+  Italian: 'it',
 };
 
 export enum FileMimeType {