refactor: extract ClipboardHandler from GeneralKeyboardIME (#426)

[prince-0408]

Description

This PR is Part 3 of 6 in modularizing GeneralKeyboardIME to resolve #426.

It extracts all clipboard monitoring, suggestion chip state, and history panel operations out of GeneralKeyboardIME.kt into a dedicated helper class: ClipboardHandler.kt.

Detailed Changes Table:

File / Component	Changes Applied	Detailed Impact
ClipboardHandler.kt [NEW]	Created dedicated helper class encapsulating clipboard state (latestClipText, hasNewClip), ClipboardMonitor callbacks, recycler view adapter setup, item deletion, and pin toggling.	+126 lines added in a modular, decoupled helper class.
GeneralKeyboardIME.kt	Delegated clipboard state properties and panel action methods (openClipboardPanel, closeClipboardPanel, hideClipboardSuggestionChip, onClipboardSuggestionClicked) to clipboardHandler.	Reduced class size by ~100 lines (from 2,808 lines down to 2,743 lines).
GeneralKeyboardIME.kt — Lifecycle Hooks	Updated onCreate(), onStartInputView(), and onFinishInputView() to trigger clipboardHandler.initClipboardMonitor(), startMonitoring(), and stopMonitoring().	Cleaned up service lifecycle methods.

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Key Benefits:

• Modularization: Isolates clipboard panel UI management, recycler view binding, and history persistence operations into ClipboardHandler.kt.
• Monolith Size Reduction: Removes ~100 lines of boilerplate and UI management code from GeneralKeyboardIME.kt.
• Zero Functional Changes: Retains exact clipboard behavior, chip visibility triggers, and database operations (ClipboardRepository).

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Related Issue

Refactors part of #426

Type of Change

• Refactoring (no functional changes, no API changes)