Fix AI quote blast rate: single formula path, correct client preview

Root cause: company-settings-lookups.js had its own baseByCfm/multiplier
tables that were completely different from ShopCapabilityCalculator.cs,
so the UI showed an inflated rate (e.g. 82 sqft/hr) while the AI prompt
received the server-computed rate (e.g. 9 sqft/hr).

- Add CompanySettingsController.DeriveBlastRate endpoint — thin GET that
  calls ShopCapabilityCalculator directly; now the single formula path
- Delete all client-side formula code (baseByCfm, multiplier tables,
  deriveBlastRate) — ~30 lines removed
- Modal live preview calls /CompanySettings/DeriveBlastRate with 250ms
  debounce instead of computing locally
- Blast setup table uses setup.derivedRate from GetBlastSetups (already
  server-computed) instead of recalculating client-side
- QuotesController.AiAnalyzeItem: when no blast setup is explicitly
  selected, fall back to the company's default blast setup so the
  configured rate is always used

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

src/PowderCoating.Web/Controllers/CompanySettingsController.cs

@@ -1726,6 +1726,26 @@ public class CompanySettingsController : Controller
 
     #region Blast Setups
 
+    /// <summary>
+    /// Single authoritative blast-rate calculation endpoint. Takes equipment parameters and
+    /// returns the sqft/hr rate using the same ShopCapabilityCalculator formula the AI uses.
+    /// The modal live preview calls this instead of duplicating the formula in JavaScript.
+    /// </summary>
+    [HttpGet]
+    public IActionResult DeriveBlastRate(decimal cfm, int nozzle, int setupType, int substrate, decimal? rateOverride)
+    {
+        var setup = new CompanyBlastSetup
+        {
+            CompressorCfm                = cfm,
+            BlastNozzleSize              = nozzle,
+            SetupType                    = (BlastSetupType)setupType,
+            PrimarySubstrate             = (BlastSubstrateType)substrate,
+            BlastRateSqFtPerHourOverride = rateOverride > 0 ? rateOverride : null
+        };
+        var rate = ShopCapabilityCalculator.GetBlastRateSqFtPerHour(setup);
+        return Json(new { rate });
+    }
+
     /// <summary>Returns all active blast setups for the current company with their derived rates.</summary>
     [HttpGet]
     public async Task<IActionResult> GetBlastSetups()