feat: multi-index refactor (shared AssetRegistry, per-vault curated constituents)

[jayeshy14]

What

Turns the protocol from a single index into a multi-index platform. The registry was conflating two jobs, the global asset catalog and one index's membership, which for a single index collapse into each other and made the separation look like ceremony. This splits them.

AssetRegistry (was ComponentRegistry)

Re-scoped to a shared global catalog of registerable assets, not an index. It is the eligible universe any index draws from: a token is registered once and any index vault may then include it.

• Renamed surface: registerAsset / removeAsset / getAsset / getAssets / assetCount, MAX_ASSETS = 250 as a catalog cap (distinct from a per-index size cap), and AssetRegistry_* errors.
• Price reads and the health-checked staleness behavior are unchanged.

IndexVault now owns its curated constituents

• Holds its own _constituents set with setConstituents, which validates each token is registered in the catalog, rejects duplicates, caps at MAX_CONSTITUENTS = 100, and caches decimals so the NAV loop makes no external decimals call.
• NAV loops over the vault's own constituents, not the whole registry.
• New public reads: getConstituents, constituentCount, isConstituent, and getHoldings, which returns each constituent's balance, USD value, and weight in bps plus the idle USD and total NAV. This is the transparency surface for "what is in the index and in what proportion."
• Membership is admin-curated, because category membership (L1, DEX, AI, and so on) is definitional rather than rank-derived. Weighting over the curated set stays autonomous.

MarketCapMethodology points at AssetRegistry; it already took constituents as arguments, so no other change.

Scope note

setConstituents is intentionally a simple owner-gated wholesale setter here. The timelock, forced-versus-discretionary removal, rate-limit, and minimum-count guardrails (spec Section 16) are a later stage, as is the deposit cap.

Testing

Adds 7 tests, including two index vaults sharing one registry with fully independent NAV (the multi-index property), getHoldings value and weight checks, idle-in-weights accounting, and setConstituents validation (unregistered asset, duplicate, set replacement). 83 tests pass; no ComponentRegistry reference remains anywhere.