Add contextual Menu and floating toolbar to EditorTab

[mcgivrer]

Editor Context Menu

Goal

Add a contextual menu (right-click) directly on the StyleClassedTextArea editor field inside DocumentTab.
The menu must reflect the common Markdown formatting actions and provide keyboard shortcut equivalents.

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Implementation location

• Class: ui/DocumentTab.java
• Target component: StyleClassedTextArea editor (RichTextFX)
• Attachment: editor.setContextMenu(createEditorContextMenu()) — same pattern as ProjectExplorerPanel.createContextMenu().
• Keyboard shortcuts: extend the existing editor.setOnKeyPressed(...) handler (currently handling Ctrl+F and Ctrl+H).

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Menu structure

Copy          Ctrl+C
Cut           Ctrl+X
Paste         Ctrl+V
──────────────────────
Title H1      Ctrl+1
Title H2      Ctrl+2
Title H3      Ctrl+3
Title H4      Ctrl+4
Title H5      Ctrl+5
Title H6      Ctrl+6
──────────────────────
Bold          Ctrl+B
Italic        Ctrl+I
──────────────────────
Insert link   Ctrl+K
Insert image  Ctrl+J

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Behaviour per entry

Copy / Cut / Paste

• Delegate directly to editor.copy(), editor.cut(), editor.paste().
• These are standard JavaFX clipboard operations — no custom logic required.
• Keyboard shortcuts: OS-native (Ctrl+C, Ctrl+X, Ctrl+V) are already handled by RichTextFX; the menu items only need to call the API methods.

Title H1 – H6 (Ctrl+1 … Ctrl+6)

• Act on the current line (no selection required).
• Algorithm:
  1. Retrieve the paragraph index at the caret: editor.getCurrentParagraph().
  2. Get the current paragraph text: editor.getParagraph(idx).getText().
  3. Strip any existing leading # characters and the optional trailing space.
  4. Prepend the appropriate prefix (#, ##, … ######) followed by a space.
  5. Replace the paragraph in-place using editor.replaceText(start, end, newLine).
• If the line already has the same heading level, toggle it off (remove the prefix).

Bold (Ctrl+B)

• Requires a non-empty selection.
• Wrap the selected text: **<SELECTION>**.
• Place the caret at the end of the wrapped text after insertion.
• If the selection is already surrounded by **, unwrap it instead (toggle behaviour).
• Item is disabled in the context menu when editor.getSelection().getLength() == 0.

Italic (Ctrl+I)

• Same toggle logic as Bold, using single asterisks: *<SELECTION>*.
• Item is disabled when no text is selected.

Insert link (Ctrl+K)

• Requires a non-empty selection which becomes the URL part of the link.
• Inserts: [<CURSOR>](<TEXT_SELECTED>) where <CURSOR> marks where the caret lands after insertion (i.e., between [ and ]).
• Concrete steps:
  1. Read String url = editor.getSelectedText().
  2. Replace selection with "[]("+url+")".
  3. Move caret to position selectionStart + 1 (inside the brackets).
• Item is disabled when no text is selected.

Warning

Keyboard conflict: Ctrl+H is already bound in DocumentTab to open the Search & Replace bar (searchReplaceBar.showSearchAndReplace()).
The original spec proposed Ctrl+H for Insert link — this would break the search feature.
Decision: use Ctrl+K for Insert link (consistent with VS Code, IntelliJ, Typora).
The Ctrl+H binding for Search & Replace is kept unchanged.

Insert image (Ctrl+J)

• Same logic as Insert link but with the image syntax.
• Inserts: ![<CURSOR>](<TEXT_SELECTED>) — caret lands at position selectionStart + 2 (inside ![ … ]).
• Item is disabled when no text is selected.

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Conditional item enabling

Set the menu's onShowing handler to enable/disable items depending on context:

contextMenu.setOnShowing(e -> {
    boolean hasSelection = editor.getSelection().getLength() > 0;
    boldItem.setDisable(!hasSelection);
    italicItem.setDisable(!hasSelection);
    insertLinkItem.setDisable(!hasSelection);
    insertImageItem.setDisable(!hasSelection);
    // Copy/Cut also require a selection
    copyItem.setDisable(!hasSelection);
    cutItem.setDisable(!hasSelection);
});

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Internationalisation

Add the following keys to every messages_*.properties file:

# Editor context menu
editor.menu.copy=Copy
editor.menu.cut=Cut
editor.menu.paste=Paste
editor.menu.heading=Title H{0}
editor.menu.bold=Bold
editor.menu.italic=Italic
editor.menu.insertLink=Insert link
editor.menu.insertImage=Insert image

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Floating toolbar (later)

Note

In a subsequent iteration, a floating toolbar will appear above the selection whenever the user selects text in the editor.
It will expose the same formatting actions (Bold, Italic, Insert link, Insert image, heading level picker) as icon buttons or a combo-box, without requiring the context menu.
Implementation hint: listen to editor.selectedTextProperty() changes; when selection becomes non-empty, compute the screen coordinates of the selection start via editor.getCharacterBoundsOnScreen(start, end) and position a Popup node accordingly.