feat(electron): main process, vault, search index, links, import, capture

Vault on plain .md files with FTS5 index, link rewriting, canvas files,
history/trash/backup, link previews, image fetch, tasks and unlinked
mentions, Notion/Obsidian importer, quick-capture window and shortcut.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

electron/capture-preload.cjs

@@ -0,0 +1,9 @@
+'use strict';
+// The quick-capture window's only bridge (electron/capture.html).
+const { contextBridge, ipcRenderer } = require('electron');
+
+contextBridge.exposeInMainWorld('capture', {
+  info: () => ipcRenderer.invoke('capture:info'),
+  save: (text, to) => ipcRenderer.invoke('capture:save', text, to),
+  close: () => ipcRenderer.send('capture:close')
+});