refactor: extract FloatingKeyboardHandler from GeneralKeyboardIME (#426)

[prince-0408]

Description

This PR is Part 1 of 6 in modularizing GeneralKeyboardIME to resolve #426.

This PR extracts all floating keyboard management, scaling calculations, resize handle handlers, and touch/drag listeners out of GeneralKeyboardIME.kt into a standalone helper class: FloatingKeyboardHandler.kt.

Key Changes in this PR (Part 1/6):

• Created FloatingKeyboardHandler: Encapsulates floating mode state (isFloatingMode), layout parameters, card theme styling, resize touch listeners, corner animations, and floating position calculations.
• Reduced Monolithic Class Size: Delegated floating mode methods in GeneralKeyboardIME.kt to floatingKeyboardHandler, shrinking GeneralKeyboardIME.kt by 550 lines (from 2,808 down to 2,259 lines).
• Zero Functional Changes: Pure refactoring that strictly preserves existing floating keyboard behavior, drag gestures, and preferences saving (PreferencesHelper).

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Refactoring Roadmap Status (#426)

• Part 1 (This PR): Extract FloatingKeyboardHandler (~550 lines removed).
• Part 2 (Next): Deduplicate isTablet() across 8 language subclasses into GeneralKeyboardIME.
• Part 3: Extract Clipboard Panel logic out of GeneralKeyboardIME into ClipboardHandler.
• Part 4: Introduce ScribeLanguage Enum to replace raw string comparisons ("English", "German").
• Part 5: Remove language-specific layout assumptions ("English", "Russian", "Swedish" -> "2x2") from base class.
• Part 6: Replace Non-Null Assertions (!!) in keyboard services with safe calls.

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Related Issue

Refactors part of #426