[DEV-008] Catch expression-level hardcoded UI strings

[chev0004]

Outline

Summary

Extends the i18n linter to catch user-facing strings hidden inside JavaScript expressions, and localizes the one leak it surfaced in the Dropdown empty state.

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Changes & Enhancements

• Type of Change:
  • Feature
  • Bugfix
  • Refactor
  • Chore
• Changes:
  • (i18n check):
    • Flag string literals assigned to user-facing object keys (label, description, placeholder, subtitle, heading, tooltip).
    • Flag ternary-rendered fallback copy, excluding class-name and identifier strings (hyphen, slash, bracket, colon) to avoid false positives.
    • Dedupe overlapping matches so a single string is reported once.
  • (dropdown):
    • Localize the Dropdown empty-state copy via a new Dropdown namespace in the en and ja locales.

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Page / App Changes

Affected Next.js Routes (Local):

Before (Screenshot)

After (Screenshot)

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Component / Storybook Changes

Affected Storybook Components (Local):

Before (Screenshot)

After (Screenshot)

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Not Doing

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Other (Remarks)

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Checklists

• Code is well-documented (comments, JSDoc, etc.).
• Existing comments were updated as needed.
• No out-of-scope changes are included.
• Write TODO comments where future work is required.
• Removed unnecessary debug code (e.g., console.log, debugger).
• Self-reviewed and tested locally.