feat: Add i18n linting rules for #3933

[akankshahu]

• Add check_missing_strings.py to verify all used translation keys exist in dict
• Add check_icu_format.py to validate ICU MessageFormat syntax and plurals
• Add check_translation_variables.py to ensure function calls have required variables
• Add lint-i18n npm script to run all i18n checks
• Add no-i18n-in-component-library ESLint rule (component-library already excluded)

All essential and good-to-have requirements from issue #3933 are now implemented.

Fixes #3933

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[Copilot]

Pull request overview

This PR introduces i18n-specific linting checks for the Mathesar UI to improve translation key hygiene and enforce formatting/usage constraints, aligning with issue #3933.

Changes:

• Add Python scripts to validate translation key presence, ICU plural/message syntax, and required variables in translation calls.
• Add an npm run lint-i18n script to run the i18n checks.
• Add a local ESLint rule intended to disallow svelte-i18n usage inside src/component-library.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
mathesar_ui/scripts/i18n/check_translation_variables.py	Adds a check that translation calls provide required ICU variables based on dict.json.
mathesar_ui/scripts/i18n/check_missing_strings.py	Adds a check that translation keys used in code exist in dict.json.
mathesar_ui/scripts/i18n/check_icu_format.py	Adds a check intended to validate ICU MessageFormat/plural syntax in dict.json.
mathesar_ui/package.json	Adds lint-i18n script to run the new/existing i18n checks.
mathesar_ui/eslint-local-rules/no-i18n-in-component-library.cjs	Introduces a local ESLint rule intended to prevent svelte-i18n usage in component-library code.

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