fix(clients): minor-age threshold to 18, senior/PWD doc reload, in-app document preview dialog

- Raise isMinor threshold from age <10 to <18 (legal definition), cascading correctly to
  guardian requirement, KYC document filtering, and Education Level/Degree Qualification
  visibility (now shown for all ages, not hidden for minors).
- Load and display previously-uploaded Senior Citizen proof / PWD certificate documents on
  edit (view/replace/remove), instead of always showing an empty upload prompt.
- Fix seniorPwdDocsComplete to accept an existing certificate, not just a freshly-picked file.
- Add DocumentPreviewDialogComponent: a reusable in-app modal (image/PDF/download) used in
  place of window.open() for saved KYC/address/senior-citizen/PWD documents — avoids popup
  blockers (fired only after the async download resolved) and Chrome/Edge's failure to paint
  large base64 data: URLs on first open.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/clients/edit-client/edit-client.component.ts

@@ -440,6 +440,26 @@ export class EditClientComponent {
           this.savingClient = false;
           this.tabEditMode[tabIndex] = false;
 
+          // Senior Citizen / PWD supporting documents — same pattern as create-client's
+          // post-creation upload, triggered here since these are plain file inputs on the
+          // General step, not part of the JSON update payload.
+          if (this.clientGeneralStep?.seniorCitizenProofFile) {
+            const seniorCitizenProofForm = new FormData();
+            seniorCitizenProofForm.append('file', this.clientGeneralStep.seniorCitizenProofFile);
+            seniorCitizenProofForm.append('name', 'seniorCitizenProof');
+            seniorCitizenProofForm.append('description', 'Senior Citizen Proof (Age/ID Proof)');
+            this.clientsService
+              .uploadClientDocument(this.clientId, seniorCitizenProofForm)
+              .subscribe({ error: () => {} });
+          }
+          if (this.clientGeneralStep?.pwdCertificateFile) {
+            const pwdCertificateForm = new FormData();
+            pwdCertificateForm.append('file', this.clientGeneralStep.pwdCertificateFile);
+            pwdCertificateForm.append('name', 'pwdCertificate');
+            pwdCertificateForm.append('description', 'Disability Certificate');
+            this.clientsService.uploadClientDocument(this.clientId, pwdCertificateForm).subscribe({ error: () => {} });
+          }
+
           // Log mobile/email changes as client notes for risk audit
           this.logFieldChangeNotes(changedFields);