fix(10-03): resolve Suggestion plugin key collision between WikiLink and Citation

Both extensions registered @tiptap/suggestion without unique pluginKey,
causing ProseMirror to throw "Adding different instances of a keyed plugin
(suggestion$)". Add distinct pluginKey values: 'wikiLinkSuggestion' and
'citationSuggestion'.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ThePyProgrammer

frontend/src/components/CitationExtension.js

@@ -258,6 +258,7 @@ export function createCitationExtension({
 
         // ── Suggestion: @ triggers autocomplete popup ────────────────────────
         Suggestion({
+          pluginKey: 'citationSuggestion',
           editor: this.editor,
           char: '@',
           allowSpaces: true,

frontend/src/components/WikiLinkExtension.js

@@ -258,6 +258,7 @@ export function createWikiLinkExtension({ getAllNotes, onWikiLinkClick }) {
 
         // ── Suggestion: [[ triggers autocomplete popup ───────────────────
         Suggestion({
+          pluginKey: 'wikiLinkSuggestion',
           editor: this.editor,
           char: '[[',
           allowSpaces: true,