fix!: index the treasury settlement chain (bps floor referrer fees)

[MehranMazhar]

Companion to clutchprotocol/clutch-node#9. Merge alongside it.

The surprise: almost nothing needed changing

The expectation going in was that the indexer would break at genesis, because the new chain puts a ChainInit transaction (RLP tag 9) in block 0 and adds chain_id to every transaction, alongside two new types (Mint tag 6, Burn tag 7) and four new balance-effect kinds.

It doesn't. Verified by inspection rather than assumed:

• ingestion.rs stores function_call_type as a raw string with an unwrap_or fallback — no exhaustive match to break.
• is_ride_function is a boolean matches!, so unknown types are simply "not ride-related".
• referrer.rs already has a tolerant _ => {} arm.
• activity.rs records unknown effect kinds with their raw string, and effect_label falls back to "Balance change".
• There is no deny_unknown_fields anywhere, so the new chain_id field is ignored.

So ChainInit/Mint/Burn and chain_id all ingest with zero parser changes. That tolerance was worth confirming explicitly, because the alternative — an enum that must be kept in lockstep with the node — would have made every future node release a two-repo change.

What actually changed

referrer.rs fee arithmetic: ceiling percent → floor basis points, using the identical formula to the node's referrer_fee_floor:

(fare as u128 * bps as u128 / 10_000) as u64

That cross-repo agreement is the point — the explorer displays the fee split, so divergent rounding would make the UI quietly disagree with on-chain state. The old ceiling rule turned 2% of a 3-unit fare into 33%; it existed only because the chain had no decimals, and it is repealed.

Plus the u8 → u16 config rename (ride_*_referrer_fee_percent → _bps) and its plumbing.

Verification

cargo test — 10/10 pass.

Note the tests were run on Rust 1.89, matching this repo's own backend/Dockerfile (ARG RUST_VERSION=1.89); 1.86 fails here because a transitive dependency requires ≥1.88, and that failure reproduces on unmodified main. Worth flagging separately: this repo commits no Cargo.lock, so its builds float on dependency resolution.

Not covered here

Live end-to-end indexing of a real Mint block needs a running treasury-break node stack; that is verified in the full-stack smoke, not in this source-only change.

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