#100 public-origin postprocessor rewrites raw and release artifact HTML

What

absolutize_social_meta() walks the whole output tree and rewrites every .html file:

src/build.rs:1312-1334:

• path.extension() == "html"
• std::fs::read_to_string(&path)?
• replace content="https://hu13.gl0w.world/og.png"

That includes committed raw HTML under raw/ and copied release artifacts under releases/<version>/, not just generated pages.

Reproduced

A repo with raw/x.html containing invalid UTF-8:

hu13 build . -o out --public-origin https://example.test
hu13: social meta read out/raw/raw/x.html: stream did not contain valid UTF-8

With valid raw HTML containing content="https://hu13.gl0w.world/og.png", the copied bytes are silently rewritten to the absolute URL. Same for release artifact HTML.

Impact

• A repo with a binary/invalid-UTF-8 .html raw file cannot build when --public-origin is set.
• /raw/ and release artifact bytes no longer match the source (breaks byte-identical downloads, hashes, and user expectations).

Fix

• Only postprocess generated page paths (or pass the absolute URL when rendering pages).
• Skip raw/, repo.git/, and releases/<version>/ artifact trees.
• Regression test: raw .html invalid UTF-8 + raw HTML marker survives unchanged; generated page still gets absolute og:image.