fix(queen): Replace broken MultilineInput with simple TextEditor

[gHashTag]

Summary

• Archived MultilineInput → MultilineInputLegacy (kept for reference)
• Added SimpleMultilineInput using pure SwiftUI TextEditor
• Removed @mention, /command, image paste features (can add incrementally)

Test Plan

• Build succeeds
• App launches without crashes
• Focus appears on click
• Typing works
• Enter sends message
• Shift+Enter inserts newline
• Multiline scroll appears

[gHashTag]

✅ Commit: 5b03a244b7

• Build succeeds
• App launches without crashes
• Manual UI testing needed for focus/typing/Enter

[gHashTag]

✅ Commit 2: f51552466d

• Fixed Enter key handling with onKeyPress
• Enter = send (default), Shift+Enter = newline
• Supports Ctrl+Enter mode via @AppStorage
• App running, ready for manual testing