Add verified Old Faithful slot index pipeline

[augustin-cheron]

Summary

• add a one-pass, no-CID repair tool for malformed Old Faithful direct slot-range indexes
• verify full CAR digests, Block CIDs, decoded Block slots, ordered membership, range limits, and atomic output publication
• stitch V2 rows from ordered slot lists and Blockzilla registries with the previous-Block off-by-one rule across epoch boundaries
• require explicit R2 targets for build-wrapper V2 uploads and document the verified prefix
• make the Old Faithful Worker use slot-index-v2-verified by default and fail closed on missing or malformed indexes
• isolate cache keys by fallback policy and make /info return an uncached 503 when verified readiness fails
• retain and document the separate CID-index dependency for out-of-line reward continuation

Verification

• cargo test --locked -p of-slot-ranges --all-targets (80 tests)
• cargo clippy --locked -p of-slot-ranges --bin of-repair-slot-ranges -- -D warnings
• cargo test --locked -p old-faithful-get-block (16 tests)
• cargo clippy --locked -p old-faithful-get-block --lib -- -D warnings
• cargo fmt --all -- --check
• git diff --check
• shell syntax checks for all three index build/sync helpers
• optimized Worker WASM build

Data rollout gate

• frozen and validated epochs 0 through 1019
• 1,020 V2 files, 19,388,160,000 bytes
• 418,689,707 indexed blocks and zero missing ranges
• 1,020 cross-epoch previous-blockhash boundary checks passed
• uploaded immutably to slot-index-v2-verified
• exact remote inventory passed
• all 1,020 objects were downloaded again and their SHA-256 values matched the local manifest

The deployed Worker is unchanged until this pull request merges and the verified-only build passes production checks.