2.0.17: feat(rich-editor): expand toolbar with free TinyMCE tools

Add preview, emoji (emoticons), special/math symbols (charmap), quote
(blockquote), a Div block format, text alignment, copy, clear-formatting
(removeformat) and strikethrough to the shared <x-gp247::rich-editor>.

All plugins ship in the self-hosted TinyMCE build (no Node/CDN - ADR-004
/ NFR-AVAIL-001); alignment/quote/copy/removeformat/strikethrough are
core buttons. Premium-only tools (WYSIWYG equation editor, Format
Painter) are intentionally excluded to keep the community build
license-free.

Ref: US-AUI-004, ADR-005, modification 20260731T052210

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>