refactor: [IOPLT-1528] Add IOTypography as single source of truth

[dmnplb]

Short description

All the typographic attributes now live in one IOTypography object in core/, which the components themselves read. Values are unchanged: the existing typography snapshots pass untouched.

Motivation

Every style pinned its attributes inside its own component, and only some of them were re-exported as loose constants. Hero is the clearest symptom: it exported heroFontSize/heroLineHeight and then ignored them. Anyone who needs a style's metrics outside a Text has had to copy the numbers and hope they stay in sync.

List of changes proposed in this pull request

• Add IOTypography in core/, with every style's font, size, line height, weight, iOS Dynamic Type ramp, letter spacing/transform and default color token
• Rewire all the typographic components to read from it
• Remove the per-style constants (h1FontSize, bodyLineHeight, …) and migrate every call site.
• Add the missing 18 value to the IOFontSize scale (referenced by MdH2)
• Add IOTypographicLinkColorToken, shared by Body, BodySmall, LabelMini and IOMarkdown
• Update both the typography README and the main README to reflect the new changes.

Important

This PR introduces breaking changes for the published package: the next DS release needs a major bump.

How to test

1. pnpm nx test @pagopa/io-app-design-system: snapshots must pass unchanged (any snapshot diff means a value drifted during the move)
2. Run the app and open Design System → Foundation → Typography: every style renders exactly as on master, in both light and dark theme
3. Check the two IDPay screens that used the old constants: Barcode result and the static code modal, including their skeleton placeholders
4. Toggle the legacy typeface: H6 still switches to 17px

[github-actions]

Jira Pull Request Link

This Pull Request refers to Jira issues:

• IOPLT-1528

[github-actions]

PR Title Validation for conventional commit type

✅ All good! PR title follows the conventional commit type.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.87%. Comparing base (b0f7d0c) to head (83f244b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8553      +/-   ##
==========================================
- Coverage   64.87%   64.87%   -0.01%     
==========================================
  Files        2000     2000              
  Lines       38247    38247              
  Branches     6531     6531              
==========================================
- Hits        24814    24812       -2     
- Misses      12004    12006       +2     
  Partials     1429     1429              

Files with missing lines	Coverage Δ
...idpay/barcode/screens/IdPayBarcodeResultScreen.tsx	91.30% <ø> (ø)
...res/idpay/common/hooks/useIDPayStaticCodeModal.tsx	94.59% <ø> (ø)

... and 1 file with indirect coverage changes

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