Update set of archived formats to: PNG, PDF, WARC

[mprpic]

Currently we only store PNG (screenshot) and WARC.

Requirements:

• Verify ArchiveBox generates PNG screenshots
• Add PDF generation capability
• Ensure WARC files are properly generated

Acceptance Criteria:

• Every successful archive contains PNG, PDF, and WARC files
• Failed format generation is logged and reported
• Archive metadata includes format availability info

[zmanion]

IME using ArchiveBox, for any given reference, some archive mechanisms work, some do not. Of course there are actual technical reasons, but sorting them all out may not be worth the effort. I suggest a minimum 30 second timeout, as I've observed certain mechanisms fail when set to 15 seconds (and work at 30). So the requirement may be to attempt PNG|PDF|WARC and then decide what an acceptable result is -- at least one of WARC or PDF? Retry?

The PNG is a "one screen" screenshot, so not the entire page.

PDFs at least used to be rather bloated, headless chrome uses (used?) Skia to generate PDF. I think this generation got better (smaller PDFs) since I started playing with ArchiveBox, but I used to run something like ps2pdf -dPDFSETTINGS=/ebook on output.pdf.