fix: correct stale min attribute and MCP wording from inventory removal

Three small leftovers from Task 7 / the inventory-quantity-tracking
removal that a final review caught:

- Edit.razor's custom-stock quantity input still had min="1" even
  though its own helper text says "Use -1 for unlimited", validation
  already accepts -1, and the add-form defaults Quantity to -1 - so
  the field rendered pre-populated with a value the browser's native
  min validation flagged as invalid. Matches the min="-1" fix already
  applied to the catalog-stock input in Task 7.
- optimize_job's MCP tool description still claimed the optimizer
  falls back to "available inventory" when no stock is configured -
  that auto-discovery fallback was removed in Task 3. An LLM reads
  this description as ground truth, so stale wording here actively
  misleads tool use. Also tightened add_job_stock's stockItemId/
  isCustomLength wording, which still said "inventory" for what is
  now just the stock catalog.
- CLAUDE.md's CutListPackingService summary said InStockBins comes
  "from inventory", nudging future readers back toward the
  auto-discovery mental model this plan removed.

CLAUDE.md

@@ -162,7 +162,7 @@ Abstract base with TPC (Table Per Concrete type) mapping — each shape gets its
 
 ### CutListPackingService
 - `PackAsync(parts, kerfInches, jobStock?)` — runs optimization per material group
-- Separates results into `InStockBins` (from inventory) and `ToBePurchasedBins`
+- Separates results into `InStockBins` (from catalog-sourced job stock) and `ToBePurchasedBins`
 - `GetSummary(result)` — calculates total bins, pieces, waste, efficiency %
 - `SerializeResult(result)` / `LoadSavedResult(json)` — JSON round-trip via DTO layer (`SavedOptimizationResult` etc.)