docs(kotlin): Tier D → Tier B (partial) after walrus fix unblock

[avrabe]

After walrus 0.26 + the legacy try/catch fix (pinned via witness #37 from the pulseengine/walrus fork; upstream PR `wasm-bindgen/walrus#316`), `witness instrument` now succeeds on Kotlin/Wasm — 54 branches captured on the leap-year fixture, was a hard panic before. Decisions stay at 0 because Kotlin emits source maps (.wasm.map V3), not DWARF — that's the next witness-side feature.

Changes

• `docs/cross-language.md`: Kotlin row Tier D → Tier B (partial). Cites chore(deps): pin walrus to pulseengine fork (legacy-catch fix, pending upstream PR #316) #37 + walrus #316 and names the remaining source-map work.
• `examples/languages/kotlin/leap-year/README.md`: "BLOCKED" → "branch-level only"; current numbers; structural caveat that source maps are weaker than DWARF (no inline chains, no address ranges).

[github-actions]

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