asset search and registry data endpoints

[mononaut]

adds two new endpoints for liquid instances:

/assets/registry/search

efficient typeahead-style substring search for liquid asset registry items, supporting query parameters:

• q: search string (max 64 characters)
• limit: max items to return (default 15, max 100)

/assets/registry/:asset

returns just the off-chain asset registry data for a specific asset ID, without the expensive history lookups.

Like the existing /assets/registry endpoint, these require --asset-db-path to be configured.

[Copilot]

Pull request overview

Adds Liquid asset registry endpoints to support faster client-side asset discovery and lightweight metadata fetches without on-chain history lookups.

Changes:

• Add /assets/registry/search for substring typeahead search with q + limit query params.
• Add /assets/registry/:asset to return off-chain registry metadata only for a given asset id.
• Implement registry-side search and add query-layer helpers for registry lookup/search.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
src/rest.rs	Adds the two new REST routes and response shaping for search results + per-asset registry lookup.
src/new_index/query.rs	Adds query methods to fetch a single registry entry and to run registry searches.
src/elements/registry.rs	Implements the underlying in-memory search across cached registry metadata fields.
src/elements/mod.rs	Re-exports AssetMeta so REST/query code can use it via crate::elements::*.

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[junderw]

A few minor things found by Copilot. Feel free to fix them if needed.

LGTM 237a2df