cat21-mint: refactor onto Cat21MintOrchestrator

The fat RxJS pipelines that lived in this component (selectedFeeRate$,
paymentOutputsForCurrentWallet$, paymentOutputs$ + its 2-pass
simulation logic) now live in the SDK's Cat21MintOrchestrator,
consumed identically by cat21.space when phase C lands.

Component shrinks from 265 lines of orchestration logic to a thin
form + view layer:

- Inject Cat21MintOrchestrator alongside the existing WalletService /
  Cat21ApiService.
- paymentOutputs$ becomes a derived map of orchestrator.simulations$:
  filter insufficient rows, sort by UTXO value desc, cap at 10 for
  the expert panel. Same surface the template already bound.
- selectedPaymentOutput stays as a component field for template
  compatibility but is two-way-bound to orchestrator.selectedUtxo:
    - paymentOutputs$ tap auto-syncs on every fresh simulation list
      (largest viable entry by default, or keep the user's pick if
      it's still viable).
    - selectPaymentOutput(row) handler updates both sides when the
      user clicks "Use this UTXO".
- mintCat21() delegates to orchestrator.mint() — the orchestrator
  recomputes the precise fee from vsize × feeRate at call time and
  dispatches to the right WalletSigner.
- Component-level booleans (utxoLoading, utxoError, mintCat21Loading,
  mintCat21Success, mintCat21Error) become read-only computed
  signals projecting orchestrator.state() / errorMessage() /
  successTxId(). Same template-facing names, same shapes; template
  references update to `name()` invocations + `*ngIf="x() as alias"`
  patterns for the two places that used optional chaining on the
  old field shape.

ngOnInit + the form's feeRate valueChanges subscription still own
the policy bits that don't belong in the SDK (minRequiredFee
validator, fastestFee default-pick, the disable-min-fee-check
escape hatch).

AOT build clean; the bundle is unchanged in size (orchestrator was
already included by the SDK bump; this commit just reorganises the
component code).

Author: hans-crypto

frontend/src/app/components/_ordpool/cat21-mint/cat21-mint.component.html

@@ -80,7 +80,7 @@ <h2 class="mt-2 mb-4">Mint a CAT-21 Ordinal</h2>
             </div>
           </div>
 
-          <div class="p-2 mt-4" *ngIf="(recommendedFees$ | async) && !selectedPaymentOutput && !utxoLoading">
+          <div class="p-2 mt-4" *ngIf="(recommendedFees$ | async) && !selectedPaymentOutput && !utxoLoading()">
             We are sorry, but we could not find find enough funds in your payment address! 😿<br>
             No UTXO has enough value to execute a transaction at the current fees.
             We recommend sending at least
@@ -102,7 +102,7 @@ <h2 class="mt-2 mb-4">Mint a CAT-21 Ordinal</h2>
             This should be enough to mint <strong class="bitcoin">multiple</strong> CAT-21 ordinals. 😻😻😻
           </div>
 
-          <div *ngIf="!utxoLoading && !utxoError && (paymentOutputs$ | async)?.length">
+          <div *ngIf="!utxoLoading() && !utxoError() && (paymentOutputs$ | async)?.length">
 
             <details>
               <summary>Show Expert Settings</summary>
@@ -123,7 +123,7 @@ <h2 class="mt-2 mb-4">Mint a CAT-21 Ordinal</h2>
                 [ngClass]="{ selected: x === this.selectedPaymentOutput }">
 
                 <button *ngIf="x !== this.selectedPaymentOutput" class="btn btn-primary float-end text-white mt-2"
-                  (click)="selectedPaymentOutput = x" type="button">
+                  (click)="selectPaymentOutput(x)" type="button">
                   Use this UTXO
                 </button>
 
@@ -166,48 +166,48 @@ <h2 class="mt-2 mb-4">Mint a CAT-21 Ordinal</h2>
           </div>
           <div class="text-center mt-4">
 
-            <button type="submit" *ngIf="!utxoLoading && !mintCat21Success" [disabled]="form.invalid || !selectedPaymentOutput"
+            <button type="submit" *ngIf="!utxoLoading() && !mintCat21Success()" [disabled]="form.invalid || !selectedPaymentOutput"
               class="btn btn-primary mt-4 mb-4 text-white">
 
-              <ng-container  *ngIf="!mintCat21Loading">
+              <ng-container  *ngIf="!mintCat21Loading()">
                 <img src="/resources/cat21-small-logo.svg" style="margin-top: -4px; margin-right: 6px"
                   title="Mint a CAT-21 ordinal" height="30"> Mint my cat
               </ng-container>
 
-              <ng-container  *ngIf="mintCat21Loading">
+              <ng-container  *ngIf="mintCat21Loading()">
                 <i class="spinner-border spinner-border-sm text-light"></i> Minting your cat
               </ng-container>
 
 
             </button>
 
-            <a href="javascript:location.reload()" *ngIf="mintCat21Success" class="btn btn-primary mt-4 mb-4 text-white">
+            <a href="javascript:location.reload()" *ngIf="mintCat21Success()" class="btn btn-primary mt-4 mb-4 text-white">
               <img src="/resources/cat21-small-logo.svg" style="margin-top: -4px; margin-right: 6px" title="Mint a CAT-21 ordinal" height="30"> Mint another cat!
             </a>
 
-          <button type="submit" disabled class="btn btn-primary mt-4 mb-4 text-white" *ngIf="utxoLoading">
+          <button type="submit" disabled class="btn btn-primary mt-4 mb-4 text-white" *ngIf="utxoLoading()">
             <i class="spinner-border spinner-border-sm text-light"></i>
             Scanning your payments address
           </button>
 
           </div>
         </form>
 
-        <div class="alert alert-success" *ngIf="mintCat21Success">
+        <div class="alert alert-success" *ngIf="mintCat21Success() as success">
           ✅&nbsp; Your CAT-21 transaction has now been submitted to the mempool.<br>
-          <ng-container *ngIf="mintCat21Success?.txId">
+          <ng-container *ngIf="success.txId">
             You can track the progress
             <a class="alert-link text-decoration-underline"
-              [routerLink]="['/tx/' | relativeUrl, mintCat21Success.txId]">here</a>.
+              [routerLink]="['/tx/' | relativeUrl, success.txId]">here</a>.
           </ng-container>
         </div>
 
-        <div class="alert alert-danger" *ngIf="mintCat21Error">
-          ❌&nbsp; {{ mintCat21Error }}
+        <div class="alert alert-danger" *ngIf="mintCat21Error() as err">
+          ❌&nbsp; {{ err }}
         </div>
 
-        <div class="alert alert-danger" *ngIf="utxoError">
-          ❌&nbsp; {{ utxoError }}
+        <div class="alert alert-danger" *ngIf="utxoError() as err">
+          ❌&nbsp; {{ err }}
         </div>
 
         <div class="alert alert-danger" *ngIf="checkerError">