fix(design-tokens): backfill generationRule for legacy semantic tokens

[ssilvius]

Summary

Existing rafters projects' on-disk semantic.rafters.json was authored before semantic.ts started writing generationRule. populateDependencyGraph requires both dependsOn AND generationRule to enter the dependency graph, so legacy semantic tokens are silently skipped at registry init -- the cascade is dormant on every project initialized before the fix shipped.

Verified in this repo: 198/198 semantic tokens in .rafters/tokens/semantic.rafters.json have generationRule = null. Setting accent to a new family via the studio API would update only the seed; every variant (-foreground, -hover, -active, -border, -ring) would stay pointing at the previous family. Designer sees a half-themed UI.

Self-heal at registry init by inferring the rule from the token name suffix and dependsOn[0] shape:

• -foreground / -text / -contrast -> contrast:auto
• -hover / -active / -focus / -disabled -> state:*
• everything else -> scale:N from value position or dependsOn[0] suffix

In-memory only -- no on-disk migration. The next normal write through the persist path picks up the backfilled rule.

Includes a small refactor: extracted parseTokenPosition() to scale-positions.ts to consolidate three inlined copies of the same regex.

Test plan

• New legacy semantic token backfill describe block in packages/design-tokens/test/semantic-cascade.test.ts
• cascades semantic tokens loaded without generationRule -- strips generationRule from generated tokens, constructs registry, cascades neutral, asserts primary + primary-hover + primary-foreground all follow
• preserves explicit generationRule when present -- regression guard so live-generated tokens still carry their explicit rule
• All 294 design-tokens tests green
• Manual studio-server verification with accent -> silver-true-honey + highlight -> silver-true-sky (pending; the broken-cascade evidence motivated this fix, in-DOM verification of the fix still owed)

🤖 Generated with Claude Code