fix(render): serve media assets with registered content types

[jrusso1020]

Render file servers currently serve AVIF, FLAC, M4A, MOV and ICO assets as application/octet-stream. Add the missing types to the active producer server used by local/distributed renders and to the public engine server helper. Full and partial producer responses now identify the media correctly while preserving its bytes.

Isolates the MIME fix reported by @fix2015 in #1836, with co-author credit. Uses the registered ICO type, image/vnd.microsoft.icon. The downloader portion is already handled on main by per-attempt partial directories and cleanup.

Validation: all ten new HTTP cases failed before the mapping fix. Afterward, 54 producer file-server tests and five engine file-server tests pass, including binary bodies and partial-response headers. Both package typechecks, lint/format, producer test classification and commit hooks pass.

[miguel-heygen]

Reviewed f60c440bb04188ba5c6b879eb77d56a0d1184853.

packages/producer/src/services/fileServer.ts:91 and packages/engine/src/services/fileServer.ts:27 add the five MIME mappings to both render servers without changing their existing case-insensitive lookup or binary response paths. packages/producer/src/services/fileServer.test.ts:319 exercises real full/range HTTP responses, and the new engine tests verify full responses and unchanged bytes. @fix2015 receives co-author credit; this ports the reported MIME fix rather than claiming new downloader functionality.

No findings. Independently reproduced all ten new cases failing with the mappings removed; at the reviewed head, 54 producer tests and five engine tests pass. Reused existing dependencies in scratch; the engine run aliases the compiler import to its exact-head HTML helper to avoid unrelated missing generated build assets. No full render/browser codec test was run. Traced local/distributed producer callers, the exported engine helper, existing Studio MIME lookup, and downloader attempt-directory cleanup.

No prior reviews or comments were present at precheck. CI has no failed checks at this check, but pending checks remain; this approval is on code/documentation merits and is not a CI-complete or merge-ready claim.

— Magi

Verdict: APPROVE
Reasoning: The change matches the current implementation and no blocking regression was found within the stated verification scope. Required CI must still finish successfully.