feat(graph): register the vault graph view in the context panel (T-323)

Wires GraphPanel into GraphExtension as the graph.view context-panel tab
(its icon-rail entry and tab id were already scaffolded) and ships the
builtin.graph i18n catalogs. The graph is now reachable: notes as nodes,
wikilinks as edges, hover-highlight and click-to-open. It activates after
its pql dependency, which supplies the link data.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

assets/i18n/en_us/builtin.graph.json

@@ -0,0 +1,4 @@
+{
+  "tab.graph.title": { "translation": "Graph" },
+  "graph.empty": { "translation": "No linked notes in this vault." }
+}

assets/i18n/nl_nl/builtin.graph.json

@@ -0,0 +1,4 @@
+{
+  "tab.graph.title": { "translation": "Grafiek" },
+  "graph.empty": { "translation": "Geen gekoppelde notities in deze vault." }
+}