Add Renovate configuration for automated dependency updates

[kantacky]

Summary

This PR introduces a Renovate configuration file to automate dependency management and keep the project's dependencies up-to-date with minimal manual intervention.

Key Changes

• Renovate setup: Added renovate.json with recommended configuration extending best practices
• Update scheduling: Configured to run dependency checks before 9am on Mondays (Asia/Tokyo timezone)
• Dependency dashboard: Enabled for visibility into all pending updates
• Semantic commits: Enabled for consistent commit message formatting
• Lock file maintenance: Enabled with weekly schedule to keep lock files current
• Smart merging strategy:
  • Non-major dev dependency updates (patch/minor) are automatically merged
  • Major version updates require manual review and are labeled for visibility
• Grouping: Non-major dev dependency updates are grouped together for easier management
• Release age requirement: Set 7-day minimum age for releases to avoid early/unstable versions

Implementation Details

• Uses bump range strategy for conservative version updates
• Applies "dependencies" label to all updates for tracking
• Disables rate limiting to ensure timely processing
• Balances automation (auto-merging safe updates) with caution (manual review for major versions)

https://claude.ai/code/session_01MgV6r4437y9zjobqWDcJou

[kantacky]

The Lint check is failing on this PR, but it's not caused by this change (the diff only adds renovate.json, which ESLint doesn't touch). The same failure reproduces identically on main at the current PR base commit (3649caf) — e.g. CI run #155 and CI run #154:

TypeError: Error while loading rule 'react/display-name': contextOrFilename.getFilename is not a function
Occurred while linting /home/runner/work/web/web/.storybook/main.ts
    at .../eslint-plugin-react/lib/util/version.js:31

This looks like an eslint-plugin-react incompatibility with eslint@10.9.1. I don't have an existing fix to port for it. I'll leave this PR as-is unless a fix lands to pull in.

---

Generated by Claude Code