Add Obsidian vault import feature (#8)

- New 'Import Obsidian' action on site settings page
- Upload a zip file of an Obsidian vault to import all notes as posts
- Markdown notes imported with title from filename, published date from
  file timestamp, and body with front-matter stripped
- Images and other attachments saved as Upload records
- New obsimport service handles zip traversal and import logic
- Unit tests for front-matter stripping

Co-authored-by: Shelley <shelley@exe.dev>

Co-authored-by: exe.dev user <exedev@kernel-leviathan.exe.xyz>
Reviewed-on: #8

views/obsimport/form.html

@@ -0,0 +1,21 @@
+<main class="container">
+  <div>
+    <h5 class="my-4">Import from Obsidian</h5>
+    <p>Select an Obsidian vault exported as a Zip file. All Markdown notes will be imported as posts, and any images or attachments will be imported as uploads.</p>
+    <form method="post" action="/sites/{{ .site.ID }}/import/obsidian" enctype="multipart/form-data">
+      <div class="row mb-3">
+        <label for="zipfile" class="col-sm-3 col-form-label text-end">Zip File</label>
+        <div class="col-sm-6">
+          <input type="file" class="form-control" id="zipfile" name="zipfile" accept=".zip">
+        </div>
+      </div>
+      <div class="row mb-3">
+        <div class="col-sm-3"></div>
+        <div class="col-sm-9">
+          <button type="submit" class="btn btn-primary">Import</button>
+          <a href="/sites/{{ .site.ID }}/settings" class="btn btn-secondary ms-2">Cancel</a>
+        </div>
+      </div>
+    </form>
+  </div>
+</main>

views/obsimport/result.html

@@ -0,0 +1,10 @@
+<main class="container">
+  <div>
+    <h5 class="my-4">Import Complete</h5>
+    <div class="alert alert-success">
+      <p class="mb-1">Successfully imported <strong>{{ .result.PostsImported }}</strong> post(s) and <strong>{{ .result.UploadsImported }}</strong> upload(s).</p>
+    </div>
+    <a href="{{ .siteURL }}" class="btn btn-primary">Go to Posts</a>
+    <a href="/sites/{{ .site.ID }}/settings" class="btn btn-secondary ms-2">Back to Settings</a>
+  </div>
+</main>

views/sitesettings/general.html

@@ -66,5 +66,12 @@
         </div>
       </div>
     </form>
+    <div class="row mb-3">
+      <div class="col-sm-3"></div>
+      <div class="col-sm-9">
+        <a href="/sites/{{ .site.ID }}/import/obsidian" class="btn btn-secondary">Import Obsidian</a>
+        <span class="form-text mx-3">Import posts and attachments from an Obsidian vault zip file.</span>
+      </div>
+    </div>
   </div>
 </main>