Add L10n helper and merge PR #3 localization into core resources

[waffensam]

Motivation

• Resolve a merge conflict around PR Localize settings and menu copy #3 by unifying localized UI copy into a shared core resource so the app and the PR changes use the same bundle for strings.
• Keep the newer branch logic and behavior while porting the PR's string changes (menu, keychain prompts, login alerts, preferences copy) into the current codebase.

Description

• Add a small localization helper L10n.tr (Sources/CodexBarCore/Localization/L10n.swift) and include Resources for the core target in Package.swift so localized strings can be loaded from CodexBarCore.
• Generate an English Localizable.strings under Sources/CodexBarCore/Resources/en.lproj/Localizable.strings containing keys required by the merged changes.
• Replace in-place literal UI strings with L10n.tr(...) across About, Menu, Keychain prompt, Preferences (General/Advanced/About/Debug/View), StatusItem login alerts, and other impacted files to centralize copy and avoid further conflicts.
• Preserve existing feature logic and provider behavior; only UI text and wiring to the new localization helper were changed.

Testing

• Ran a basic repository check (git diff --check) which reported no whitespace/merge issues.
• Ran pnpm check (lint script) and it failed due to the environment attempting to download SwiftFormat from GitHub and receiving HTTP 403, so automated linting could not complete.
• Attempted swiftformat / swiftlint and swift test, but these commands were unavailable or failed because the environment cannot fetch SwiftPM/GitHub dependencies (network 403), so full build/test and the ./Scripts/compile_and_run.sh packaging run could not be completed here.

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Codex Task