Make search result text selectable and copyable

[saberoueslati]

Description

Closes #825

This PR makes text inside Search Results rows selectable and copyable without changing the existing copy-all behavior. Individual result text can now be selected with the mouse and copied as plain text via Ctrl+C, Edit > Copy, or the right-click context menu. The toolbar copy button still copies all search results.

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Changes

src/docks/SearchResultsDock.cpp

• Added an embedded read-only QTextEdit for individual search result rows so result text can be selected directly.
• Added plain-text copy support for selected result text, without copying highlight formatting.
• Added result-row context menu support for Copy and Copy Selected Line.
• Added Copy Selected Line to the tree row context menu so right-clicking the line-number cell also supports copying the full result line.
• Preserved double-click activation so opening/navigating to a search result still works.
• Clears previous result-text selection when left-clicking in Search Results.
• Updates embedded result text widget fonts when the configured editor font changes.
• Kept the existing toolbar copy button behavior for copying all search results.

src/docks/SearchResultsDock.h

• Added copySelectedResultText() so the main window copy action can copy selected Search Results text when appropriate.
• Added event filtering and selection-clearing helpers for result text selection handling.

src/dialogs/MainWindow.cpp

• Updated Edit > Copy to first copy selected Search Results text when a result-text selection exists, then fall back to the current editor copy behavior.

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Manual Testing

• Ran a search and selected part of an individual result row.
• Verified Ctrl+C copies only the selected result text as plain text.
• Verified Edit > Copy copies selected result text even after opening the Edit menu.
• Verified the result text right-click menu Copy copies selected text.
• Verified Copy Selected Line copies the full result line from the result text context menu.
• Verified Copy Selected Line is also available when right-clicking the line-number cell.
• Verified the toolbar copy button still copies all search results.
• Verified double-clicking a result still navigates to the match.

Video of basic manual test below:

Screencast.from.2026-06-08.23-04-01.webm