feat(map-tokens): kind-scope the candidate list in the prompt

[Tyler Pina (tylerpina)]

Summary

• The map tokens step's prompt gave every design-token prop the entire DTCG token tree as candidates, regardless of the prop's own $token.kind — a color prop saw spacing, typography, and every other tier too. That's noise on every run and a truncation risk on real libraries where each token category is separately populated.
• The token path index is now split into one section per $token.kind present among the CDF's design-token props, each scoped to tokens of that type only, and flattened to one path · type line per candidate instead of a nested JSON array — legible and countable. A prop with no $token.kind still falls back to the full, unscoped tree, unchanged from before.
• Candidate ordering within a section is sorted by path for deterministic output on repeated runs over identical input.
• No change to apply.ts, the map_token_prop contract, or the CDF schema — this only reshapes what the agent sees before it decides.

Test plan

• Added tests in prompt-builder.test.ts: kind-scoping excludes other kinds, a prop with no $token.kind falls back to the full tree, multiple distinct kinds render separate sections, and a determinism check (identical input produces a byte-identical prompt across repeated calls).
• Full experience-design-system-generation suite passes (152 tests).
• Full experience-design-system-cli suite passes against a freshly rebuilt dist (3234 tests) — the CLI's map-tokens integration tests spawn the compiled binary, so this exercises the change end-to-end, not just the unit tests.

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