🛡️ Sentinel: [HIGH] Fix XSS in event preview formatting

[kevinaboos]

🚨 Severity: HIGH
💡 Vulnerability: Cross-Site Scripting (XSS) / HTML injection via unsanitized Matrix event previews. User-controlled text such as custom event types, custom guest access rules, custom history visibility, custom join rules, aliases, and canonical aliases were directly embedded into formatted strings in src/event_preview.rs and rendered as HTML without escaping.
🎯 Impact: An attacker could inject malicious HTML or script tags into the application by setting crafted custom rules, aliases, or sending messages with malicious event types. When a user views the timeline, the unsanitized preview could execute arbitrary code or corrupt the UI, potentially compromising their session.
🔧 Fix: Updated text_preview_of_other_state and text_preview_of_other_message_like to properly escape the relevant string values using htmlize::escape_text whenever format_as_html is true. text_preview_of_other_message_like was also updated to accept the format_as_html parameter and all its call sites were adjusted accordingly.
✅ Verification: Ran cargo check, cargo clippy, and cargo test --lib successfully. Reviewed the code to ensure htmlize::escape_text is correctly applied to the user-controlled strings and that lifetimes are managed correctly (e.g. using Cow::Borrowed when escaping is not needed and allocating where necessary).

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PR created automatically by Jules for task 7387762487924466894 started by @kevinaboos

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