Support compiling the library for wasm32

[l1n]

What

Makes the glowpub library compile for wasm32-unknown-unknown, enabling in-browser epub generation. The CLI binary is unchanged and remains native-only.

• The networking, filesystem-cache, and auth modules (api, cached, auth) are gated behind cfg(not(target_arch = "wasm32")), along with their dependencies (reqwest, tokio, glob, clap, simple_logger, rpassword), which move to a target-specific dependency table.
• Thread::to_epub / Continuity::to_epub are split: the async native half downloads images as before, then delegates to a new sync to_epub_from_images(options, HashMap<String, InternedImage>), which is available on wasm so callers can supply images fetched by other means (e.g. JS fetch). to_epub_remote_images is untouched.
• intern_images keeps InternedImage and its pure image-processing methods on wasm; only the download-and-intern async functions are native-gated.
• getrandom's JS backends are enabled for wasm32 (rand and uuid pull it in transitively).

Building

RUSTFLAGS='--cfg getrandom_backend="wasm_js"' cargo check --lib --target wasm32-unknown-unknown

(--lib because the CLI binary doesn't build on wasm; getrandom_backend is required by getrandom 0.3 on wasm32-unknown-unknown.)

Motivation / testing

I run an RSS/epub mirror (glowficrss.com) that uses the glowpub CLI server-side. For access-locked threads the server has no credentials, so it now falls back to a page that fetches the thread through the user's own glowfic login and assembles the epub in the browser with this library compiled to wasm (via a small wasm-bindgen wrapper crate that parses the raw API JSON into Post/Reply and calls to_epub_from_images). That path is running in production: output is byte-identical to the native path for the threads I compared, with icons interned, covers rendered (the bundled Cinzel font makes this work without system fonts), and the result readable in Calibre and Apple Books.

cargo check/cargo test pass natively; cargo check --lib passes for wasm32 as above.

🤖 Generated with Claude Code

[l1n]

Pushed two follow-ups: current stable clippy (1.96) fails the existing -D warnings gate on five pre-existing collapsible_ifs in cached.rs (if-let chains are stable now), so those are collapsed in their own commit; and the commented-out wasm CI steps in check.yml are enabled — the CLI moved to src/cli.rs with a stub main on wasm32 so the whole workspace clippy-checks cleanly for wasm32-unknown-unknown without --lib.

[QuartzLibrary]

Hi! Really cool to see this running in a third party service. :D

wasm is actually something I have wanted to do. Hope you don't mind, but I pushed an alternative implementation at #67.

Would you mind checking it does what you you need it to before I merge it?

[QuartzLibrary]

Closed in favor of #67.