feat(attachments): importer dispatch — archive extract + non-media capture

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_importer.py

@@ -117,13 +117,14 @@ def test_transparent_filter(importer, import_layout):
 
 
 def test_unsupported_extension(importer, import_layout):
+    # FC-2d-iii: non-media is no longer skipped — it's captured as a
+    # PostAttachment so nothing a post contained is lost.
     import_root, _ = import_layout
     src = import_root / "Alice" / "notes.txt"
     src.parent.mkdir(parents=True, exist_ok=True)
     src.write_text("hello")
     result = importer.import_one(src)
-    assert result.status == "skipped"
-    assert result.skip_reason == SkipReason.invalid_image
+    assert result.status == "attached"
 
 
 def test_root_level_file_has_no_artist(importer, import_layout):