fix: resolve token references in rounded and spacing sections

[tejas100]

Summary

Fixes #25

Token references in rounded and spacing sections were never resolved
into their respective Maps. Only the colors section had a Phase 2
resolution pass. This meant any valid token reference like {rounded.sm}
or {spacing.base} was silently dropped from the Tailwind export with no
error or warning emitted.

Root Cause

In model/handler.ts, Phase 1 stores unresolved references in symbolTable
only — they are never added to the rounded or spacing Maps. Unlike
colors, there was no Phase 2 pass to resolve them.

Fix

Added Phase 2 resolution passes for rounded and spacing, mirroring
the existing pattern used for colors.

Tests

Added 7 new test cases to model/handler.test.ts covering:

• Direct token reference resolution in rounded
• Chained token reference resolution in rounded
• Direct token reference resolution in spacing
• Chained token reference resolution in spacing
• Symbol table correctness after resolution
• End-to-end propagation into component resolution

All 201 tests pass.

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[davideast]

Thank you so much @tejas100!