refactor: delete stale files and consolidate .mindmodel structure

Deleted stale root-level Python files:
- main.py (unused 'Hello world' script)
- verify.py (unused table info script)
- scraper.py (unused MotionScraper class)
- scheduler.py (unused DataUpdateScheduler class)

Deleted duplicate .mindmodel root YAML files (subdirectory versions are more comprehensive):
- anti-patterns.yaml, architecture.yaml, conventions.yaml
- dependencies.yaml, domain.yaml, domain-glossary.yaml
- stack.yaml, tech-stack.yaml, workflows.yaml

Added comprehensive .mindmodel subdirectories:
- constraints/ (naming, db-schema, error-handling, types, etc.)
- patterns/ (api, architecture, database, python, streamlit, etc.)
- examples/ (code examples for each pattern)
- anti-patterns/, architecture/, conventions/, dependencies/, domain/, stack/

Updated ARCHITECTURE.md to reflect current codebase:
- Removed references to non-existent files
- Added missing files (explorer.py, explorer_helpers.py, pipeline/)
- Added directory structure documentation
- Updated tech stack to include scipy, sklearn, umap

Updated .gitignore:
- Added patterns for generated analysis files
- Added .worktrees/ pattern (was already in gitignore but dir was deleted)

Removed empty .worktrees/ directory

.mindmodel/conventions/conventions.yaml

@@ -0,0 +1,124 @@
+# Naming Conventions
+
+## Files
+- **snake_case** for all Python files: `database.py`, `explorer_helpers.py`, `motion_cache.py`
+- **PascalCase** NOT used for files
+
+## Functions
+- **snake_case**: `get_svd_vectors()`, `compute_party_coords()`, `build_scatter_trace()`
+- Private helpers prefixed with `_`: `_get_window_data()`
+
+## Classes
+- **PascalCase**: `MotionDatabase`, `Config`
+- **Dataclass pattern** for Config: `@dataclass` decorator with typed fields
+
+## Variables
+- **snake_case**: `party_map`, `mp_name`, `svd_vectors`, `party_centroids`
+- **CONSTANT_SNAKE_CASE** for module-level constants: `PARTY_COLOURS`, `DEFAULT_WINDOW`
+
+## Module-Level Exports
+- **Singleton instance**: `db = MotionDatabase()` at module bottom (not class-level)
+- **Config instance**: `config = Config(...)` at module bottom
+- **Dicts**: `PARTY_COLOURS` exported from `config.py`
+
+---
+
+# Error Handling
+
+## Known Patterns
+1. **Bare except with pass** (ANTI-PATTERN - see anti-patterns.yaml)
+   ```python
+   except:
+       pass  # database.py:47
+   ```
+
+2. **Graceful degradation**: catch specific exceptions, fall back to default
+   ```python
+   try:
+       result = compute_svd()
+   except ImportError:
+       result = DEFAULT_SVD
+   ```
+
+3. **Optional dependency fallbacks**:
+   ```python
+   try:
+       import umap
+       use_umap = True
+   except ImportError:
+       use_umap = False
+   ```
+
+4. **Nested exception handling** (ANTI-PATTERN - see anti-patterns.yaml):
+   ```python
+   try:
+       ...
+   except Exception:
+       try:
+           ...
+       except Exception:
+           pass
+   ```
+
+## Rules
+- Never use bare `except:` — always specify exception type
+- Never swallow exceptions silently — log or return a sensible default
+- For optional deps, use `ImportError` or `ModuleNotFoundError` explicitly
+- Avoid nested try/except blocks
+
+---
+
+# Code Organization
+
+## Singleton Pattern
+Each module owns one shared instance:
+```python
+# database.py
+db = MotionDatabase()
+
+# config.py
+config = Config(...)
+PARTY_COLOURS = {...}
+```
+
+## Pure Functions in Helpers
+`explorer_helpers.py` contains only pure functions (no IO, no Streamlit calls):
+```python
+def compute_party_coords(svd_vectors, party_map):
+    """Pure: no side effects, no imports from this module"""
+    ...
+
+def build_scatter_trace(df, color_col):
+    """Pure: returns Plotly trace dict"""
+    ...
+```
+
+## Cached Data Loaders
+Use `@st.cache_data` for expensive data loading:
+```python
+@st.cache_data
+def load_svd_vectors(window: str) -> pd.DataFrame:
+    return db.get_svd_vectors(window)
+```
+
+## Dataclass Config
+```python
+@dataclass
+class Config:
+    db_path: str = "data/stemwijzer.duckdb"
+    default_window: str = "2023"
+    party_colours: dict = field(default_factory=lambda: PARTY_COLOURS)
+```
+
+---
+
+# Imports
+
+## Ordering (convention)
+1. Standard library
+2. Third-party (streamlit, ibis, plotly, sklearn, umap)
+3. Local/relative imports
+
+## Avoid
+- Wildcard imports (`from module import *`)
+- Circular imports (ensure dependency direction: helpers → database → config)