feat: use session localization git submodule

[Aerilym]

See: https://github.com/session-foundation/session-localization

[Copilot]

Pull request overview

This PR migrates the localization system to use a git submodule for the session-localization library. The change consolidates localization logic into a shared library while simplifying the test codebase.

Key Changes:

• Replaced local localization files with a git submodule reference
• Added automation script to sync localization commits between session-desktop and session-playwright
• Updated import statements to reference the submodule

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/localization/locales.ts	Removed ~5700 lines of generated locale definitions, now provided by submodule
tests/localization/lib	Added as git submodule pointing to session-localization repository
tests/localization/englishStrippedStr.ts	Updated imports to use submodule exports
tests/localization/constants.ts	Removed file, constants now provided by submodule
tests/localization/Localizer.ts	Removed ~512 lines of localization logic, now provided by submodule
tests/automation/enforce_localized_str.spec.ts	Updated imports to use submodule exports
sync-localization.sh	New script to synchronize submodule commits between repositories
package.json	Added "sync" script command
.tool-versions	Specified Node.js version 20.18.2
.gitmodules	Configured git submodule for session-localization

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