Create/update skills to support migration and document a plan

[andrewscfc]

I'm part way through this but thought I'd drop an AI summary below to aid review.

I've been prompting and refining a migration plan geared around AI automation. I've heavily refined .github/skills/convert-webcore-component/SKILL.md and docs/SCSS-Modules-Migration.mdx but .github/skills/migrate-component-to-scss-modules/SKILL.md is still a work in progress

I haven't carefully reviewed this summary, will do it again before full review

Summary

Adds the AI tooling to carry out the SCSS Modules migration, plus a plan for how the work is sequenced.

Stacked on #14073 — its changes appear in this branch but belong to that PR.

Changes

.github/skills/migrate-component-to-scss-modules/SKILL.md (new)
The step-by-step process for taking a component off Emotion: an Emotion-to-SCSS value lookup, triage checks for components that can't be migrated by a styling change alone, and per-batch verification steps.

.github/skills/convert-webcore-component/SKILL.md (updated)
This skill told agents to produce index.styles.ts files and Emotion css props. Left unchanged it would work against the standards merged in #14280, so the styling half is rewritten for SCSS Modules. TypeScript guidance is untouched.

docs/SCSS-Modules-Migration.mdx (new)
Sequencing plan for engineers — scope, batching principles, blocked components, and a dated starting batch order. Published to Storybook, and deliberately outside the paths agents read so it can hold planning detail without consuming their context.

Worth discussing: should we add clsx?

Emotion's css={[base, cond && modifier]} silently drops falsy entries. className doesn't, so the direct translation renders class="link false" — a silent bug. This shape appears in 11 components.

The skills currently require a ternary with an empty-string fallback and say not to add a dependency, following our "avoid new dependencies" rule. I lean towards adding clsx instead — ~200 bytes, and it removes the footgun across ~30 migrations rather than relying on everyone getting the ternary right. If we agree, both skills need updating.

Notes

The blocked-component list and batch ordering were derived from the codebase rather than assumed. That turned up two components which look like easy early wins but aren't: MostRead/Label passes a css prop into a psammead component and uses a palette value as a runtime prop, and RelatedContentSection imports a legacy Emotion styles file directly.

[andrewscfc]

not really reviewed this file properly yet