rust(docs): name asset_ids in list_runs output and fix list_channels asset fields

[alexa-sift]

Description

The list_runs description said each run includes asset_id/asset_name, but runs carry asset_ids and no asset name. Agents that projected those fields with fields got nothing back and had to list runs again. The description now names asset_ids, drops "annotation state" (a filter-only field), and says to resolve names with list_assets. The fields help now warns that filter fields are not output fields.

list_channels had the same problem: it promised asset_name and "units". It now names asset_id and unit_id and points to list_assets for the asset name.

New tests confirm list_runs returns asset_ids and list_channels returns asset_id/unit_id when requested with fields, and that asset_name lands in unmatched_fields.

Verification

• cargo fmt -p sift_mcp, cargo clippy -p sift_mcp --all-targets --all-features (no new warnings), cargo test -p sift_mcp (580 pass)