fix(callout): strip title continuation backslash

[oldwinter]

Summary

• Obsidian callout titles keep a trailing continuation backslash (e.g. 提示).
• First-party markdown rewrite in createFileParser after plugin textTransforms strips trailing \ from [!TYPE] opener lines only. Body lines and vault notes are unchanged.

Why not vault edits: the trailing \ is valid Obsidian title continuation; publishing should strip it for all [!TYPE] titles without rewriting 花园导览 / 本库使用指南.

Closes #26

Verify

• 花园导览 and 本库使用指南 info callout title shows 提示, not 提示\
• Callout body unchanged
• npx tsx --test quartz/util/calloutTitle.test.ts

UI: 闻测 must screenshot 本库使用指南 and 花园导览 callout titles on a real device and comment on this PR. No screenshot = not done.

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[netlify]

❌ Deploy Preview for aquamarine-salamander-b041fe failed. Why did it fail? →

Name	Link
🔨 Latest commit	5b5dec0
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[oldwinter]

Blocking review at exact head 5b5dec069a91732eb37475e1ee0aad1b7aaca5b8:

1. The regex removes an entire trailing backslash run, erasing literal escaped backslashes instead of only a continuation slash.
2. Raw preprocessing rewrites callout-looking text inside fenced code and also runs when callout parsing is disabled.
3. Valid callouts indented up to three spaces are not recognized, so their body can remain folded into the title.
4. The changed test file fails Prettier and omits escaped-run parity, fenced code, indentation and parser integration.

Unblock action: move the fix into Markdown-aware callout processing, preserve escape parity/disabled/fenced content, support valid indentation, and add formatted integration tests. Issue #26 remains open.