feat: make media inspection progressive

docs/KNOWN_LIMITATIONS.md

@@ -45,6 +45,9 @@ FFmpeg output does not remove these product/browser/resource limits.
   presets from runtime formats/codecs/encoders/filters.
 - FFmpeg-readable output may be download-only because browser media elements
   support fewer container/codec combinations.
+- Browser-native basic information intentionally omits codecs, complete stream
+  lists, chapters, tags, subtitles, attachments and dispositions. Features
+  that need those details request an authoritative local FFprobe pass.
 - Browser support, codec policy and memory differ across Chromium, Firefox and
   Safari and across desktop/mobile versions.
 - The reviewed 0.12.10 core profile passes the non-empty Opus encode/re-probe
@@ -83,9 +86,11 @@ FFmpeg output does not remove these product/browser/resource limits.
   together; development-only smoke artifacts must not be distributed.
 - Chromium covers a broad real pinned-core ST operation matrix, a real MT
   H.264/AAC conversion, MT-to-ST fallback, nested static/Toolbox-context
-  loading and one two-size ST/MT performance baseline. Firefox, Safari, mobile,
-  exhaustive MT feature parity and repeated performance measurements remain
-  unrecorded. Live Portal container/header verification is a deployment gate.
+  loading and one two-size ST/MT performance baseline. Firefox covers the
+  opt-in large-file browser-metadata/playback-to-authoritative-probe
+  regression. Broad Firefox operation parity, Safari, mobile, exhaustive MT
+  feature parity and repeated performance measurements remain unrecorded. Live
+  Portal container/header verification is a deployment gate.
 
 See `docs/FORMAT_SUPPORT.md`, `docs/PERFORMANCE.md`,
 `docs/PORTAL_REQUIREMENTS.md` and `docs/RELEASE.md` for testable detail.