fix: sync TermFormDialog state when switching between edit targets

[JiayuuWang]

Summary

Fixes #220

When clicking Edit on different taxonomy terms, the form dialog retains data from the previously edited term because React.useState only uses its initial value on first mount — subsequent prop changes don't update state automatically.

• Add a useEffect in TermFormDialog that resets all form fields (label, slug, parentId, description, autoSlug, error) whenever the term prop changes
• This ensures the form always shows the correct data for the currently selected term

Steps to reproduce the bug

1. Go to Taxonomies > Categories
2. Click Edit on "Category A" — form shows Category A's data ✓
3. Close the dialog without saving
4. Click Edit on "Category B" — form still shows Category A's data ✗ (bug)

After this fix, step 4 correctly shows Category B's data.

Test plan

• Click Edit on a term → form shows correct data
• Close dialog, click Edit on a different term → form updates to show new term's data
• Slug auto-generation is disabled when editing an existing term (autoSlug = false)
• Slug auto-generation is enabled for new terms (Add button)
• Error state is cleared when switching between terms

🤖 Generated with Claude Code

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