feat(chains): add TVL by asset command via DefiLlama

[ggonzalez94]

Summary

• add chains assets command to expose chain-level TVL broken down by asset
• implement MarketDataProvider.ChainsAssets and DefiLlama adapter support
• require DEFI_DEFILLAMA_API_KEY for chains.assets capability and surface it in provider metadata
• add deterministic sorting/aggregation and canonical asset_id population when known
• document key requirement in README/AGENTS and add changelog entries

API / Contract

• new command: defi chains assets --chain <chain> [--asset <asset>] [--limit N]
• new model row fields: rank, chain, chain_id, asset, asset_id, tvl_usd
• no breaking changes to existing commands or envelope contract

Validation

• go test ./...
• go test -race ./...
• go vet ./...
• smoke: defi chains top --limit 2 --results-only
• smoke: defi chains assets --chain 1 --asset USDC --results-only without key returns auth error (exit code 10)

---

Note

Medium Risk
Adds a new CLI surface area and a DefiLlama Pro API integration that is key-gated and involves parsing/aggregating loosely typed JSON, which could cause edge-case failures if the upstream payload shape changes.

Overview
Adds a new defi chains assets command that returns chain-level TVL broken down by asset (optionally filtered via --asset) and caches results with the same 5m TTL as other chain/protocol lookups.

Implements MarketDataProvider.ChainsAssets plus a DefiLlama-backed adapter that requires DEFI_DEFILLAMA_API_KEY, aggregates breakdown categories, sorts deterministically, and fills asset_id when the token is known. Updates provider capability metadata, adds the ChainAssetTVL model + tests, and documents the new command and key requirement in README.md/AGENTS.md/CHANGELOG.md.

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