docs: README v0.1.7.1 — correct doc count, results table, dual-metric

[Lawrenzho-bit]

Changes

• Fix wrong doc count: "200 documents" → 59 documents (v0.1.7; v0.2 target was aspirational)
• Fix stale comment: "v0.1 ships 5 samples" → 59-doc index (v0.1.7)
• Remove unimplemented claim: "held-out split rotated quarterly"
• Add Current results table (v0.1.7.1 chrF · oracle-layout) — the first thing any reviewer looks for
• Add dual-metric note (chrF + COMET-Kiwi) with key finding on COMET–chrF gap
• Update repository layout block to reflect three data subdirs (annotations/, flores_derived/, rileykim_derived/)
• Update license section to mention CC-BY-SA-4.0 for FLORES-derived docs
• Link methodology-roadmap.md from metrics section

Test plan

• CI passes
• README renders correctly on GitHub (especially the results table and code blocks)

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