refactor: simplify Explorer to 3 focused tabs — compass, trajectories, SVD

Removes embedding-heavy search and generic browser tabs from the Explorer.
The project does not currently use embeddings meaningfully, so the similarity
search and browser features were dead weight.

Changes:
- explorer.py: Remove search and browser tabs, keep compass/trajectories/SVD
- explorer.py: Remove fused_embeddings and similarity_cache stats from sidebar
- Home.py: Update Explorer description to match new focused layout
- analysis/tabs/__init__.py: Remove search and browser exports
- tests: Update decomposition and import tests for new tab set

Result: Explorer now has 3 focused analytical tabs instead of 5.

tests/test_explorer_decomposition.py

@@ -27,8 +27,6 @@ class TestExplorerDecomposition:
         tabs = [
             ("analysis/tabs/compass.py", "build_compass_tab"),
             ("analysis/tabs/trajectories.py", "build_trajectories_tab"),
-            ("analysis/tabs/search.py", "build_search_tab"),
-            ("analysis/tabs/browser.py", "build_browser_tab"),
             ("analysis/tabs/components.py", "build_svd_components_tab"),
             ("analysis/tabs/quiz.py", "build_mp_quiz_tab"),
         ]
@@ -75,8 +73,6 @@ class TestExplorerDecomposition:
         tab_modules = [
             "analysis/tabs/compass.py",
             "analysis/tabs/trajectories.py",
-            "analysis/tabs/search.py",
-            "analysis/tabs/browser.py",
             "analysis/tabs/components.py",
             "analysis/tabs/quiz.py",
             "analysis/tabs/_rendering.py",

tests/test_explorer_import.py

@@ -9,6 +9,5 @@ def test_explorer_importable():
     assert callable(mod.run_app)
     assert hasattr(mod, "load_positions")
     assert hasattr(mod, "load_motions_df")
-    assert hasattr(mod, "query_similar")
-    assert hasattr(mod, "build_compass_tab")
-    assert hasattr(mod, "build_search_tab")
+    assert hasattr(mod, "build_svd_components_tab")
+    assert hasattr(mod, "build_mp_quiz_tab")