Compile log: errors / warnings filtering and folding

[Oaklight]

Problem

Compile log is raw latexmk output. Errors are buried among hundreds of font / package warnings.

Proposed

• Parse log into structured entries: errors, warnings, badbox, info
• Toggle filters at top of log panel (Errors / Warnings / All)
• Collapse uninteresting blocks (Underfull \hbox, font substitution chatter)
• Pairs naturally with Jump to source line from compile log errors #9 (jump-to-error from log) — same parser

Notes

Probably best landed together with #9.

Priority: P3