feat(invite-funnel): set real Android app signing cert fingerprint

Replace the assetlinks.json placeholder with the Play App Signing key
SHA-256 certificate fingerprint so Android App Links for
https://sauci.app/join/* can verify.

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

apps/web/public/.well-known/assetlinks.json

@@ -5,7 +5,7 @@
       "namespace": "android_app",
       "package_name": "com.sauci.app",
       "sha256_cert_fingerprints": [
-        "PLACEHOLDER_ANDROID_RELEASE_SHA256_CERT_FINGERPRINT"
+        "65:2F:E7:60:3F:2E:D2:54:8B:4A:EF:0E:F1:AC:35:3E:DD:13:13:EF:35:E7:90:A7:01:1F:89:0F:4F:71:E2:21"
       ]
     }
   }

apps/web/public/.well-known/well-known.test.ts

@@ -23,8 +23,8 @@ describe('assetlinks.json', () => {
 
     expect(data[0].target.package_name).toBe('com.sauci.app')
     expect(data[0].target.namespace).toBe('android_app')
-    // The real release cert fingerprint is not present in this repository;
-    // this placeholder must be replaced before Android App Links will verify.
-    expect(data[0].target.sha256_cert_fingerprints[0]).toContain('PLACEHOLDER')
+    // Must be the Play App Signing key certificate fingerprint (Play Console >
+    // Test and release > Setup > App signing), colon-separated uppercase hex.
+    expect(data[0].target.sha256_cert_fingerprints[0]).toMatch(/^([0-9A-F]{2}:){31}[0-9A-F]{2}$/)
   })
 })