fix: exclude .laputa-cache.json and settings.json from vault git tracking

These files are machine-specific and should never be committed or cause
conflicts when syncing vaults across devices.

Changes:
- init_repo() now writes .gitignore with .laputa-cache.json and
  .laputa/settings.json excluded before the first commit
- .DS_Store and common editor artifacts also excluded
- openConflictFileRef falls back to openLocalFile() for non-note files
  so 'Open in editor' works for .json conflict files (opens in system
  default app, e.g. TextEdit/VS Code)
- Removed stale git.rs (replaced by git/mod.rs from refactor)
- 2 new Rust tests for .gitignore creation behavior

src/App.tsx

@@ -45,6 +45,7 @@ import { isTauri, mockInvoke } from './mock-tauri'
 import type { SidebarSelection, VaultEntry } from './types'
 import type { NoteListItem } from './utils/ai-context'
 import { filterEntries } from './utils/noteListHelpers'
+import { openLocalFile } from './utils/url'
 import './App.css'
 
 // Type declaration for mock content storage
@@ -287,8 +288,13 @@ function App() {
       const fullPath = `${resolvedPath}/${relativePath}`
       const entry = vault.entries.find(e => e.path === fullPath)
       if (entry) {
+        // Markdown note — open inside Laputa editor
         notes.handleSelectNote(entry)
         dialogs.closeConflictResolver()
+      } else {
+        // Non-note file (e.g. .laputa-cache.json, settings.json) —
+        // open with system default app so the user can inspect/edit it
+        openLocalFile(fullPath)
       }
     }
   }, [resolvedPath, vault.entries, notes, dialogs])

src/utils/url.ts

@@ -22,3 +22,11 @@ export async function openExternalUrl(url: string): Promise<void> {
     window.open(url, '_blank')
   }
 }
+
+/** Open a local file path with the system default app (e.g. TextEdit for .json). */
+export async function openLocalFile(absolutePath: string): Promise<void> {
+  if (isTauri()) {
+    const { openPath } = await import('@tauri-apps/plugin-opener')
+    await openPath(absolutePath)
+  }
+}