feat: add core clipboard infrastructure (1/5)

[bniladridas]

Part of clipboard image support feature (#5316)

This PR replaces the large PR #10136 which was closed due to size concerns as requested by @jacob314.

Chunk 1 of 5 - Core clipboard infrastructure and key bindings

What's included:

• Cross-platform clipboard image detection (macOS, Windows, Linux)
• Paste protection with size limits and content validation
• Content hashing for duplicate detection and timing controls
• Clipboard state management with processing flags
• Enhanced key bindings to support both Ctrl+V and Command+V
• Automatic cleanup of old clipboard images

Dependencies:

None - this is the foundation chunk

Next chunks:

• Chunk 2: Testing infrastructure
• Chunk 3: Screenshot support
• Chunk 4: UI integration
• Chunk 5: E2E tests & documentation

Addresses part of #5316

[gemini-code-assist[bot]]

Summary of Changes

Hello @bniladridas, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request lays the foundational core clipboard infrastructure, serving as the first chunk of a larger feature to support clipboard images. It replaces a previously closed large PR by breaking down the work into manageable parts. The primary goal is to enable robust, cross-platform handling of clipboard content, particularly images, with built-in protection, state management, and improved keybinding support.

Highlights

• Cross-Platform Clipboard Infrastructure: Introduces core infrastructure for detecting and saving clipboard images across macOS, Windows, and Linux, moving beyond the previous macOS-only support.
• Paste Protection and Validation: Implements robust paste protection mechanisms, including configurable size limits, content type validation, and custom validation functions to enhance security and control over pasted content.
• Clipboard State Management: Adds a new clipboard state management system that uses content hashing to prevent duplicate processing of the same clipboard content within a defined interval, improving efficiency and preventing redundant operations.
• Enhanced Key Bindings: Updates key bindings to support both Ctrl+V (for Windows/Linux) and Command+V (for macOS) for the PASTE_CLIPBOARD_IMAGE command, ensuring a consistent user experience across different operating systems.
• Automatic Cleanup: Includes functionality for automatic cleanup of old temporary clipboard image files, preventing accumulation and managing disk space.

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[bniladridas]

yes of course, i will address your grounded review suggestions shortly.