Add duplicate style name detection across categories in configurator

[Claude]

When tokens across different categories resolve to the same effective style name (style ?? name), the generated Swift code produces duplicate static properties on ShapeStyle, causing compiler errors. The configurator now detects and warns about these conflicts.

Changes

• validation.js: Added findDuplicateStyleName() to compare effective style names across all enabled categories, returning the conflicting category name
• state.svelte.js: Exported getAllStyles() to provide validation access to all token data
• TokenTag.svelte: Integrated duplicate detection using Svelte 5's $derived for reactive updates; shows warning icon and tooltip identifying the conflicting category
• TokenPopover.svelte: Displays inline warning message when duplicates detected: "Style name .{name} is already used by another token in {Category}. This will cause a compiler error."
• TokenField.svelte: Passes category context to enable proper duplicate detection

All conflicts (both SwiftUI built-ins and cross-category duplicates) use the same visual treatment: red outline/background with warning icon.

Example conflict scenario that now shows warnings:

{
  "colors": ["surface"],
  "gradients": [{"name": "vibrant", "style": "surface"}]
}

Both tokens now highlight with warnings since they both resolve to .surface.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.30%. Comparing base (8d7ff17) to head (4cb7f9c).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main       #7   +/-   ##
=======================================
  Coverage   99.30%   99.30%           
=======================================
  Files          28       28           
  Lines        1154     1154           
=======================================
  Hits         1146     1146           
  Misses          8        8           

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