M7: find fonts that macOS font managers activate outside the font folders

Font managers such as RightFont, FontBase and Typeface keep fonts in their
own library folders and activate them through Core Text, without copying
them into /Library/Fonts or ~/Library/Fonts. Every other Mac app lists
these fonts; FigCraft walks only the font folders, so it didn't, and a
file using one of them drew in a fallback font.

On macOS the scan now also asks Core Text for the file of every available
font and indexes the files that lie outside the walked folders. All three
scans (the first, the on-demand one and text.rescanFonts) share this, so a
font activated while the app runs is found by a rescan like a newly
installed one.

Core Text needs unsafe FFI, which the workspace forbids, so the query goes
through the safe wrappers of the core-text crate, pinned at =20.1.0. That
version builds on the core-foundation 0.9, core-graphics 0.23 and
foreign-types 0.5 the lockfile already has: core-text is the only new
package. The call sits inside catch_unwind, so anything unexpected from
Core Text leaves the scan with the font folders alone. Other platforms are
unchanged.

On a Mac with RightFont, 15 families from its library are now listed
(Geist, JetBrains Mono, Clash Display and others) that weren't before. A
full font listing went from 0.06 s to 0.20 s on that machine.

Tests: the filter that keeps files outside the font folders once, indexing
a font file found outside them, and (macOS only) that Core Text lists the
system's font files. cargo test --workspace, cargo clippy -p figcraft-text
--all-targets -D warnings and cargo fmt --check pass on macOS 15. CI
builds on Linux only, so the macOS path is checked locally.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit 5699e7abe6)

docs/cli.md

@@ -25,6 +25,12 @@ On Linux and other Unix systems except macOS, user fonts are read from
 `$XDG_DATA_HOME/fonts`, or `$HOME/.local/share/fonts` when `XDG_DATA_HOME` is unset,
 empty or relative. The legacy `$HOME/.fonts` directory is also scanned.
 
+On macOS the font folders (`/System/Library/Fonts`, `/Library/Fonts`, `~/Library/Fonts` and the
+system's downloadable fonts) are read, and so is every other font file Core Text lists as
+available: fonts a font manager such as RightFont, FontBase or Typeface activates from its own
+library, without copying them into a font folder. Fonts activated while the app runs are found by
+`text.rescanFonts`, like newly installed ones.
+
 On macOS, fonts activated through Adobe Fonts are read where Creative Cloud keeps them
 (`~/Library/Application Support/Adobe/CoreSync/plugins/livetype`), so they're available while
 they're active there. Files without an extension are read when they start like a font file.