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/pricelist.md

@@ -0,0 +1,112 @@
+# Pricelists
+
+## Types
+
+PriceForge supports three pricelist types (`source` field):
+
+| Type | Data source | Status |
+|------|-------------|--------|
+| `estimate` | `qt_lot_metadata` — snapshot of current prices | Active |
+| `warehouse` | `stock_log` — stock import data | Active |
+| `competitor` | B2B marketplace APIs | Reserved |
+
+---
+
+## Estimate
+
+**Source**: snapshot of current component prices from `qt_lot_metadata`.
+
+**Stores**:
+- `price_period_days` — price calculation window
+- `price_coefficient` — markup coefficient
+- `manual_price` — manually set price
+- `meta_prices` — historical prices
+
+**Purpose**: primary pricelist for calculations and estimates.
+
+**Categories**: loaded from `lot.lot_category` for each component.
+
+---
+
+## Warehouse
+
+**Source**: `stock_log` (stock import records).
+
+**Rules (CRITICAL)**:
+
+1. **Only mapped partnumbers** — only positions with a record in `lot_partnumbers` are included. Unmapped partnumbers must not appear in any form.
+2. **No pricing settings** — do not load from `lot_metadata`: no `price_period_days`, `price_coefficient`, `manual_price`, `meta_prices`.
+3. **Price method**: always `weighted_avg` (quantity-weighted average).
+4. Field `price_method` always contains `"weighted_avg"`.
+5. These are raw stock prices without additional processing.
+
+**Categories**: loaded from `lot.lot_category`.
+
+**Implementation**: `internal/warehouse/snapshot.go`
+
+---
+
+## Competitor
+
+Reserved for future integration with B2B marketplace APIs (automated quotes).
+
+---
+
+## Data Model
+
+```go
+type Pricelist struct {
+    ID      uint   `gorm:"primaryKey"`
+    Version string
+    Source  string // "estimate" | "warehouse" | "competitor"
+    // ...
+}
+
+type PricelistItem struct {
+    ID          uint    `gorm:"primaryKey"`
+    PricelistID uint
+    LotName     string  `gorm:"size:255"`
+    Price       float64 `gorm:"type:decimal(12,2)"`
+    LotCategory *string `gorm:"column:lot_category;size:50" json:"category,omitempty"`
+
+    // Virtual fields (via JOIN or programmatically)
+    LotDescription string   `gorm:"-:migration" json:"lot_description,omitempty"`
+    AvailableQty   *float64 `gorm:"-" json:"available_qty,omitempty"`
+    Partnumbers    []string `gorm:"-" json:"partnumbers,omitempty"`
+}
+```
+
+> `gorm:"-:migration"` — no DB column created, but mapped on SELECT.
+> `gorm:"-"` — fully ignored in all DB operations.
+
+---
+
+## Categories (lot_category)
+
+- **Source**: `lot.lot_category` column in table `lot`.
+- **NOT** from `qt_lot_metadata`.
+- **NOT** derived from LOT name.
+- Persisted into `qt_pricelist_items.lot_category` when pricelist is created.
+- JSON field name: `"category"`.
+- JOIN with `lot` is only needed for `lot_description`; category is already in `qt_pricelist_items`.
+- Default value when category is missing: `PART_`.
+
+---
+
+## Pricelist Creation (background task)
+
+Creation runs via Task Manager. Handler returns `task_id`; frontend polls.
+
+```
+POST /api/pricelists/create
+→ { "task_id": "uuid" }
+→ polling GET /api/tasks/:id
+→ { "status": "completed", "result": { "pricelist_id": 42 } }
+```
+
+Task type: `TaskTypePricelistCreate`.
+
+**Implementation**:
+- Service: `internal/services/pricelist/service.go`
+- Warehouse calc: `internal/warehouse/snapshot.go`
+- Handler: `internal/handlers/pricelist.go`