fix(reader): select imported custom fonts

[codedogQBY]

Analysis

• 导入本地字体文件不成功 #107 reports that importing a local font does not visibly add/apply the font.
• The import flows saved the font but left the reader on the previous selected font, so users had to manually find and select the new font after import.
• Newly imported local/direct-url fonts also derived CSS font-family names from the display name, which can include CJK characters, spaces, or punctuation. That makes the generated @font-face and iframe CSS less robust.
• On mobile, Android document pickers can return content:// URIs; the Expo platform file read path only handled the new File API path directly.

Changes

• Add a stable ReadAnyCustomFont-... family helper and use it for newly imported local/direct-url fonts.
• Let addFont(font, { select: true }) add and select a font in one store update, avoiding async index write races.
• Auto-select fonts after desktop/mobile local import, direct URL import, and preset add.
• Preserve the original picked filename when saving font files so the extension stays correct.
• Quote custom font-family values consistently in app and reader @font-face CSS.
• Add an Android content:// fallback for Expo readFile.
• Load local mobile fonts into Expo Font for the settings-list preview when possible.
• Explicitly clear mobile reader custom font settings when the user switches back to system default.

Verification

• pnpm --filter app exec tsc --noEmit
• pnpm --filter @readany/app-expo exec tsc --noEmit
• git diff --check
• pnpm exec biome check --write ... applied safe formatting/import fixes; full targeted check still exits non-zero on existing lint in touched files, including pre-existing label/htmlFor, noForEach/non-null assertion, and no-explicit-any diagnostics.

Fixes #107