Make table insertion disablable via Lexxy.configure (tables: false) or a tables element attribute. The default stays true, preserving current behavior.

When disabled: the TablesExtension is not registered (dropping the table nodes, table commands, and the figure/tbody import allow-list), the table toolbar button is hidden via the data-tables attribute, the lexxy-table-tools controls are not created, and insertTable no-ops. Table markup is reduced to plain text on import.

Make color highlighting disablable via Lexxy.configure (highlight: { enabled: false }) or a highlight element attribute. The default stays enabled, preserving current behavior. Both the object form { enabled: false } and a bare highlight: false are accepted.

When disabled: the HighlightExtension (toggle/remove commands, the <mark> import converter, paste canonicalizers) is not registered, the toolbar highlight dropdown is hidden via a data-highlight attribute, the dropdown setup is guarded, and highlight markup is reduced to plain text on import — both <mark> (by dropping the conversion) and legacy Trix styled elements (em/strong/span/del keep their bold/italic/strikethrough but lose the highlight color).

Make the inline marks (bold, italic, strikethrough, underline) configurable
via Lexxy.configure or a `marks` element attribute, as an allow-list. The
default enables all four, preserving current behavior. Accepts a JSON array
(marks='["bold","italic"]') or a whitespace-separated string (marks="bold
italic"); pass [] to disable every mark.

A disabled mark is inert everywhere, not just hidden from the toolbar: its
FORMAT_TEXT_COMMAND is swallowed by a high-priority interceptor (covering the
toolbar button, programmatic dispatch, and the native Cmd+B/I/U shortcuts), its
Markdown shortcut transformers are filtered out, its toolbar button is hidden
via a data-disabled-marks attribute, and its semantic tags are dropped from the
HTML import conversions so saved markup is reduced to plain text on load and
paste. A TextNode transform additionally clears any disabled-mark format bit
restored from pasted Lexical clipboard data.

# Conflicts:
#	app/assets/stylesheets/lexxy-editor.css
#	docs/configuration.md
#	src/elements/editor.js
#	test/dummy/app/views/posts/_form.html.erb

# Conflicts:
#	src/config/lexxy.js
#	src/elements/editor.js
#	test/dummy/app/views/posts/_form.html.erb

# Conflicts:
#	app/assets/stylesheets/lexxy-editor.css
#	src/config/lexxy.js
#	src/elements/editor.js

New sandbox template that mirrors /sandbox/empty but disables the features
FetLife does not use: code, highlight, and tables, and restricts inline marks
to bold, italic, and strikethrough (no underline).

Integrates the headings configuration option (basecamp#754) and wires it
into the editor, which the PR left unimplemented. A new headings.js holds the
canonical heading levels; the toolbar's format menu, active-state, and the
native editor-initialized event are driven by the configured "headings" array.
Adds an H1 ("Huge") heading level: toolbar button, icon, and the
setFormatHeadingHuge command. Defaults remain h2/h3/h4 so existing behavior is
unchanged. Markdown heading shortcuts stay unrestricted.

Copying between Lexxy editors carries an application/x-lexical-editor payload
whose styled text nodes are deserialized directly, bypassing the <mark> import
conversion that strips highlight from HTML. A disabled-highlight editor then
rendered the pasted color. Add a TextNode transform (registered only when
highlight is disabled) that clears color/background-color styles and the
highlight format bit, mirroring the disabled-mark stripper.