One-call agent context: composition + media + transcript + brand

Everything an authoring agent needs to open a project, in ONE read: the active composition (with its format and markers hoisted), the project's media pool with a hasTranscript flag per item, the first transcribed item's word-timed transcript, and the brand kit bound to the project. Replaces the get_composition + get_media_context + get_profile opening sequence. A freshly created project reads back with composition: null — that is the empty state, not an error; 404 means the project doesn't exist for your org. Transcript BODIES are never inlined per media item — read another item's with GET /v1/media/{id}/transcript, and its faces/beat/word grids with GET /v1/media/{id}/context. The media pool is capped at 50; mediaPagination reports whether more exists. Continue with paginated GET /v1/media?projectId=... (list_media in MCP) to see the rest.