v0.2.0

feat: UPnP Search action (v0.2.0)

Add optional Search to the MediaServer: a ContentProvider.search() hook, the
Search SOAP action + SCPD declaration, real GetSearchCapabilities (advertised
only when the provider implements search — empty otherwise, the spec signal that
stops control points from searching), and a parseSearchCriteria helper that
extracts free-text terms + a coarse item/container class filter from the raw
UPnP SearchCriteria grammar. Browse/Search share one response builder.

Verified end-to-end over SOAP: SCPD declares Search, GetSearchCapabilities
returns the fields, and a Search request reaches provider.search with the
container id and unescaped criteria.