Migrate to Tailwind default font weight classes

[kmcginnes]

Description

Removes the custom fontWeight override from tailwind.config.ts and migrates all class usages to Tailwind's standard weight vocabulary. Zero visual change — the rendered CSS weight values are identical.

Old class	New class	CSS weight
font-base	font-normal	400
font-bold	font-semibold	600
font-extraBold	font-bold	700

font-light (300) and font-medium (500) already matched their Tailwind defaults and required no change.

This restores the full default weight scale (thin/extralight/light/normal/medium/semibold/bold/extrabold/black) for future use, and removes one more piece of JS config ahead of the full config file deletion (#1954).

How to read

1. tailwind.config.ts — the fontWeight block deletion
2. index.css — @apply font-bold → font-semibold on the <b> element
3. Remaining 22 files — mechanical font-base → font-normal, font-bold → font-semibold class renames

Validation

• pnpm checks passes
• pnpm test passes (2178 tests)
• Visual: no change — same CSS weight values under standard Tailwind names

Related Issues

• Closes Migrate to Tailwind default font weight classes #1961
• Part of Define design system and align codebase styling #1952
• Blocking Delete tailwind.config.ts and migrate to CSS-native declarations #1954

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.