Add an editor context menu for selected text

[Arham Amin (arhxam)]

Fixes #854.

Summary

Right-clicking inside the current text selection now opens a small in-editor context menu with Cut, Copy, Paste, Select All, and Find. The menu reuses Edit's existing command, localization, clipboard, and TUI menu primitives, so the actions behave the same as their Edit-menu and keyboard-shortcut equivalents.

The popup follows the click position, flips toward the viewport when opened near the right or bottom edge, supports normal keyboard focus, and closes on Escape, command activation, or focus loss. Right-clicks outside a selection keep the existing behavior.

Test plan

• cargo test -p edit --bin edit draw_editor::tests::right_clicking_selected_text_opens_context_menu -- --nocapture
• cargo test --workspace
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings

The regression test creates a real selection, delivers a right-mouse event through the TUI input path, and verifies the rendered popup contains each requested localized command.

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