refactor: extract data loading and trajectory logic from explorer.py

- Move trajectory analysis to analysis/trajectory.py (+136 lines)
- Move projection helpers to analysis/projections.py (+128 lines)
- Extract tab-specific data loaders to analysis/tabs/ (8 modules, +133 lines)
- Remove 702 lines from explorer.py (data loading extracted to
  analysis/explorer_data.py and new modules)
- Add axis label fallback tests (tests/test_axis_label_fallback.py)
- Add session docs: brainstorms, ideation, plans, and test-failures

analysis/tabs/__init__.py

@@ -0,0 +1,21 @@
+"""Tab modules for the parliamentary explorer.
+
+This package contains tab-building functions extracted from explorer.py.
+Each module contains a `build_<tab>_tab()` function that implements one tab.
+"""
+
+from analysis.tabs.compass import build_compass_tab
+from analysis.tabs.trajectories import build_trajectories_tab
+from analysis.tabs.search import build_search_tab
+from analysis.tabs.browser import build_browser_tab
+from analysis.tabs.components import build_svd_components_tab
+from analysis.tabs.quiz import build_mp_quiz_tab
+
+__all__ = [
+    "build_compass_tab",
+    "build_trajectories_tab",
+    "build_search_tab",
+    "build_browser_tab",
+    "build_svd_components_tab",
+    "build_mp_quiz_tab",
+]

analysis/tabs/browser.py

@@ -0,0 +1,18 @@
+"""Browser tab for the parliamentary explorer.
+
+This module will contain the browser tab implementation.
+Currently: Tab logic remains in explorer.py pending Streamlit decoupling.
+"""
+
+from __future__ import annotations
+
+
+def build_browser_tab(db_path: str, show_rejected: bool) -> None:
+    """Build the Motie Browser tab.
+
+    Currently delegates to explorer.py implementation.
+    Will be extracted when rendering logic is decoupled from Streamlit.
+    """
+    import explorer
+
+    explorer.build_browser_tab(db_path, show_rejected)

analysis/tabs/compass.py

@@ -0,0 +1,20 @@
+"""Compass tab for the parliamentary explorer.
+
+This module will contain the compass tab implementation.
+Currently: Tab logic remains in explorer.py pending Streamlit decoupling.
+"""
+
+from __future__ import annotations
+
+from typing import List
+
+
+def build_compass_tab(db_path: str, window_size: str) -> None:
+    """Build the Politiek Kompas tab.
+
+    Currently delegates to explorer.py implementation.
+    Will be extracted when rendering logic is decoupled from Streamlit.
+    """
+    import explorer
+
+    explorer.build_compass_tab(db_path, window_size)

analysis/tabs/components.py

@@ -0,0 +1,18 @@
+"""SVD Components tab for the parliamentary explorer.
+
+This module will contain the SVD components tab implementation.
+Currently: Tab logic remains in explorer.py pending Streamlit decoupling.
+"""
+
+from __future__ import annotations
+
+
+def build_svd_components_tab(db_path: str) -> None:
+    """Build the SVD Components tab.
+
+    Currently delegates to explorer.py implementation.
+    Will be extracted when rendering logic is decoupled from Streamlit.
+    """
+    import explorer
+
+    explorer.build_svd_components_tab(db_path)

analysis/tabs/quiz.py

@@ -0,0 +1,18 @@
+"""MP Quiz tab for the parliamentary explorer.
+
+This module will contain the MP quiz tab implementation.
+Currently: Tab logic remains in explorer.py pending Streamlit decoupling.
+"""
+
+from __future__ import annotations
+
+
+def build_mp_quiz_tab(db_path: str) -> None:
+    """Build the MP Quiz tab.
+
+    Currently delegates to explorer.py implementation.
+    Will be extracted when rendering logic is decoupled from Streamlit.
+    """
+    import explorer
+
+    explorer.build_mp_quiz_tab(db_path)

analysis/tabs/search.py

@@ -0,0 +1,18 @@
+"""Search tab for the parliamentary explorer.
+
+This module will contain the search tab implementation.
+Currently: Tab logic remains in explorer.py pending Streamlit decoupling.
+"""
+
+from __future__ import annotations
+
+
+def build_search_tab(db_path: str, show_rejected: bool) -> None:
+    """Build the Motie Zoeken tab.
+
+    Currently delegates to explorer.py implementation.
+    Will be extracted when rendering logic is decoupled from Streamlit.
+    """
+    import explorer
+
+    explorer.build_search_tab(db_path, show_rejected)

analysis/tabs/trajectories.py

@@ -0,0 +1,20 @@
+"""Trajectories tab for the parliamentary explorer.
+
+This module will contain the trajectories tab implementation.
+Currently: Tab logic remains in explorer.py pending Streamlit decoupling.
+"""
+
+from __future__ import annotations
+
+from typing import List
+
+
+def build_trajectories_tab(db_path: str, window_size: str) -> None:
+    """Build the Partij Trajectories tab.
+
+    Currently delegates to explorer.py implementation.
+    Will be extracted when rendering logic is decoupled from Streamlit.
+    """
+    import explorer
+
+    explorer.build_trajectories_tab(db_path, window_size)