v0.6.11: detect China TC260 AIGC PNG chunk + HuggingFace hf-job-id

v0.6.11: detect China TC260 AIGC PNG chunk and HuggingFace hf-job-id

New provenance signals

Auditing a 646-image corpus surfaced two markers the library previously reported
as Unknown. identify now catches both:

• China TC260 AIGC label as a PNG tEXt chunk. Doubao (ByteDance) and other
  China-served generators also write the mandatory TC260 label as a raw-JSON
  AIGC PNG chunk, with no namespaced XMP marker. aigc_label now reads both
  serializations (the XMP <TC260:AIGC> block and the PNG chunk) via a shared
  parser, gating the PNG path on a known TC260 field so a generic AIGC key
  cannot false-positive. 28 corpus files now resolve as AI (high confidence).
• HuggingFace-hosted job marker (hf-job-id). HuggingFace Jobs / Spaces
  stamp generated PNGs with an hf-job-id chunk. It marks the hosting job, not
  a model (commonly diffusion output), so it lifts an Unknown verdict to a
  tentative AI at medium confidence, parallel to the visible sparkle and
  never overriding a hard metadata signal. 3 corpus files.

Both markers are stripped on removal (the PNG save whitelist keeps only standard
metadata keys) and surfaced by has_ai_metadata / get_ai_metadata.