docs: update CHANGELOG with font MIME mode, compatibility layer, and diagnostics

Summarize the font MIME mode setting, the standardized setting compatibility layer, and the unredacted media root path added to task diagnostics.

Author: Masterain98

CHANGELOG.md

@@ -15,9 +15,12 @@ All notable changes follow Keep a Changelog categories.
 - Conservative source-audio filtering with manual track overrides and exact output verification.
 - Safe plan editing, external track reassignment/order, subtitle metadata editing, and ffmpeg audio previews.
 - Persistent SQLite task queue/history, crash interruption state, retries, replanning, and per-task diagnostics.
+- Task diagnostics now expose the unredacted media/project root path so troubleshooting agents can locate the original media resources.
 - Validated persistent font-subset cache and ffmpeg/libass render integration tests.
 - Opt-in update checks and post-verification Plex library refresh with environment-only token handling.
 - English/Simplified Chinese CLI messages with stable JSON output and error contracts.
+- Font attachment MIME mode setting (`font.mime_mode`) letting users choose the legacy (`application/x-truetype-font`, `application/vnd.ms-opentype`) or modern (`font/ttf`, `font/otf`, `font/collection`) MIME scheme written into MKV files.
+- Standardized setting compatibility layer (`plexmuxy/compatibility.py`) that declares each version-gated setting's required tool version in a compact notation (e.g. `mkvmerge>=66`); the GUI now automatically disables options whose environment requirements are unmet (the modern font MIME mode requires mkvmerge v66+).
 - Fixed-identity Windows installer, restricted notification activation, SBOM, release manifest, optional signing, and PyPI Trusted Publishing workflow.
 
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