Add icons and large size to TagField

[pglevy]

Closes #161

Summary

• Add optional icon / iconPosition (START | END, default START) to TagItem, using Lucide icons (matches ButtonWidget's pattern)
• Icon color has no separate prop — it inherits the tag's text color via currentColor
• Add LARGE tag size (SMALL | STANDARD | LARGE; no MEDIUM, per SAIL docs)
• Text sizes for LARGE align with buttonSizeMap's text-xl, but vertical padding stays shallow so tags keep their pill shape instead of growing to button height
• When an icon is present, the icon-adjacent side's horizontal padding is tightened by 2px (inline style override) for visual balance — the icon's own weight plus the text/icon gap otherwise made that side look heavier
• Moved tag sizing into tagSizeMap / tagIconSizeMap / tagHorizontalPaddingMap in src/utils/sailMaps.ts, consistent with the shared-map convention already used for buttons

Testing

• New src/components/Tag/TagField.test.tsx — 29 tests covering visibility, rendering, sizing, icons (position, color inheritance, invalid icon name, size scaling), the new padding adjustment, and accessibility (list/listitem roles, aria-hidden icons, accessible name from visible text)
• New stories: LargeSize, WithIcons, IconSizes
• Full suite: 499/499 tests pass
• pnpm run lint: 0 errors (pre-existing warnings elsewhere, unrelated)
• pnpm run build:lib: type-checks and builds cleanly
• Verified visually in Storybook

Notes

• Found a pre-existing a11y gap unrelated to this change: linked tags have role="listitem" which overrides the anchor's implicit link role. Not fixed here since it's out of scope — happy to file a follow-up issue if useful.