docs: add bible/ as single source of architectural truth

- Created bible/ with hierarchical documentation (architecture, pricelists,
  vendor mapping, background tasks, data rules, patterns, API, operations, history)
- CLAUDE.md reduced to one instruction: read and follow the bible
- README.md reduced to quick start only
- Removed MEMORY.md and csv_export.md (content consolidated into bible/)
- Fixed stale facts found during audit: weighted_avg (not weighted_median),
  correct API route names (/export-csv, /recalculate-all)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bible/data-rules.md

@@ -0,0 +1,51 @@
+# Data Rules
+
+## Component Categories (lot_category)
+
+### Source
+
+Categories are **always** taken from `lot.lot_category` (table `lot`).
+
+**NOT** from `qt_lot_metadata`.
+**NOT** derived from the LOT name or article name.
+
+### When creating pricelists
+
+1. **Estimate**: load `lot.lot_category` for all components.
+2. **Warehouse**: load `lot.lot_category` for all positions.
+3. Persist into `lot_category` column of `qt_pricelist_items`.
+
+### Model
+
+```go
+type PricelistItem struct {
+    LotCategory *string `gorm:"column:lot_category;size:50" json:"category,omitempty"`
+    // JSON field is "category" for the frontend
+}
+```
+
+### Rules
+
+- Category is **not** a virtual field — it is persisted to DB when the pricelist is created.
+- JOIN with `lot` is only needed for `lot_description`; category is already in `qt_pricelist_items`.
+- Default value when category is absent in source: `PART_`.
+
+---
+
+## Price Method
+
+- Warehouse pricelist: `price_method` = `"weighted_avg"` (quantity-weighted average).
+- Estimate pricelist: method determined by per-component settings.
+
+---
+
+## Warehouse: Filtering by lot_partnumbers
+
+**Rule (CRITICAL)**: only positions with a matching record in `lot_partnumbers` are included in the warehouse pricelist. Unmapped partnumbers are completely excluded.
+
+---
+
+## Component Data Source
+
+- Source: MariaDB (not SQLite).
+- `handlers/component.go` uses `componentService.List()` (MariaDB).