feat(chat): add delete-all-versions action for multi-version messages

[luosc]

Rename the message deletion entry to "Delete This Version" and expose a separate "Delete All Versions" action whenever the current message group has more than one stored version. Keep the existing single-version delete path unchanged for messages without alternate versions.

Route the new action through the shared chat content layer so both mobile and desktop menus use the same version-aware behavior. Add explicit confirmation copy for deleting the current version versus deleting the entire message version group, and persist version selection cleanup when a group is removed entirely.

Update localized strings across all four ARB files, regenerate l10n output, and add focused tests for menu visibility and version-selection recomputation after single-version and all-version deletion flows.

Closes #437

Files:

• lib/features/chat/widgets/message_more_sheet.dart: extend MessageMoreAction, add canDeleteAllVersions, rename the delete action to current-version semantics, and show a separate Delete All Versions entry on both mobile and desktop menus.
• lib/features/home/widgets/message_list_view.dart: pass version-count awareness into the more-actions sheet and route deleteCurrentVersion vs deleteAllVersions to separate callbacks.
• lib/features/home/pages/home_page.dart: add separate confirmation dialogs and action routing for deleting the current version versus deleting all versions in a message group.
• lib/features/home/controllers/home_page_controller.dart: add a controller entry point for deleting all versions in a message group and clear translation UI state for every removed version.
• lib/features/home/controllers/home_view_model.dart: unify version deletion logic, add deleteAllMessageVersions, compute the next selected version after removals, and remove stale selection state when a message group is deleted entirely.
• lib/core/services/chat/chat_service.dart: add clearSelectedVersion so persisted conversation version selections are removed when a message group no longer exists.
• lib/l10n/app_en.arb: rename delete strings to current-version wording and add all-version delete labels and confirmation copy.
• lib/l10n/app_zh.arb: add the same current-version/all-version delete wording in Chinese.
• lib/l10n/app_zh_Hans.arb: add the same current-version/all-version delete wording in Simplified Chinese.
• lib/l10n/app_zh_Hant.arb: add the same current-version/all-version delete wording in Traditional Chinese.
• lib/l10n/app_localizations.dart: regenerate localization interface for the new delete strings.
• lib/l10n/app_localizations_en.dart: regenerate English localization output.
• lib/l10n/app_localizations_zh.dart: regenerate Chinese localization output for zh / zh_Hans / zh_Hant.
• test/message_more_sheet_test.dart: verify that the menu shows Delete All Versions only when multiple versions exist.
• test/home_view_model_version_selection_test.dart: verify version-selection recomputation after deleting an earlier version, deleting the selected version, and deleting all versions.

[luosc]

@Chevey339 已经更新到最新基线了