Move HTML→Markdown and Unicode-abuse sanitization into Post

[odrobnik]

Summary

• Bumps SwiftText minimum version to 1.1.7 (required for SwiftTextCore product)
• Adds SwiftTextCore to the PostServer target
• Moves Unicode-abuse sanitization fully into Post
• Sanitizes subject and body output across CLI, MCP, and IDLE hook payloads
• Adds optional unicodeAbuse description to JSON/MCP/hook outputs when sanitization modified content

Motivation

SwiftMail's MessagePart.markdownContent() (which performed HTML→Markdown + sanitization) is being removed in the companion PR Cocoanetics/SwiftMail#remove-swifttext. Post already owned HTMLToMarkdown via SwiftTextHTML; this PR completes the move by also preserving Unicode-abuse sanitization inside Post itself.

Oliver also wanted sanitization to apply consistently anywhere Post exposes extracted content — not just markdown conversion — and to surface a simple machine-readable/human-readable hint when content had to be cleaned.

Behavior

Sanitization

UnicodeAbuseSanitizer now removes abusive Unicode from exported content, including:

• bidirectional override/isolate control characters (e.g. U+202E)
• excessive combining marks (zalgo-style clusters)
• suspiciously long ZWJ sequences
• abusive Unicode tag sequences

Covered outputs

This now applies to:

• CLI fetch (text, html, and markdown body modes)
• CLI eml (text, html, and markdown body modes)
• CLI list --json and search --json
• CLI plain-text subject/header display
• IDLE hook payload subject + markdown
• MCP listMessages
• MCP searchMessages
• MCP fetchMessage
• reply quoting via draft --replying-to

New metadata

When sanitization modifies subject and/or body, outputs may include:

"unicodeAbuse": "Subject: Removed bidirectional control characters; Body: Trimmed excessive combining marks"

No field is emitted when nothing had to be changed.

Notes

• Raw RFC822 fetch remains raw by design
• This keeps IMAP flags semantically separate from local content-analysis results
• Existing output shapes remain largely intact; the main additive schema change is optional unicodeAbuse

Build / test

swift build -c release ✅
swift test ✅ (8 tests, 0 failures)