Correct SDK-integration docs and add license-gating walkthrough

Fixes surfaced by the onboarding test harness, each verified against the
published SDKs and the daemon:

- integrate.html: real v0.3 verify() shape (throws/Err, returns
  VerifyOk{payload,...}, no `valid` bool; LicensingError `.code` in TS,
  `.kind` in Python; Rust Error::BadSignature/BadFormat). Offline-expiry
  and server-side key-transport notes; corrected the admin-API table
  (licenses list needs product_id; added the /search row).
- agent.html: merchant-onboard role row; product/policy-create workflows;
  buyer_note -> note; find-by-email -> /search; the worked-example
  walkthrough; code blocks restyled to the pre.code design contract.
- wire-format.html: corrected the GET /v1/issuer/public-key response shape.

wire-format.html

@@ -117,10 +117,11 @@ MCowBQYDK2VwAyEAmz7q8r4t1v…h3k2pXq9wL
     <p>This is the same encoding that <code>openssl pkey -pubout</code> produces. Keysat exposes it at <code>GET /v1/issuer/public-key</code>:</p>
 
     <pre class="code">{
-  <span class="s">"public_key_pem"</span>: <span class="s">"-----BEGIN PUBLIC KEY-----\n…\n-----END PUBLIC KEY-----\n"</span>,
-  <span class="s">"public_key_b64"</span>: <span class="s">"mz7q8r4t1v…h3k2pXq9wL"</span>,
-  <span class="s">"fingerprint_hex"</span>: <span class="s">"feed face cafe babe …"</span>
+  <span class="s">"key_algorithm"</span>: <span class="s">"ed25519"</span>,
+  <span class="s">"key_format_version"</span>: <span class="n">2</span>,
+  <span class="s">"public_key_pem"</span>: <span class="s">"-----BEGIN PUBLIC KEY-----\n…\n-----END PUBLIC KEY-----\n"</span>
 }</pre>
+    <p>The <code>public_key_pem</code> field is the one you embed in your app. Verification needs only the PEM; the SDKs parse it with <code>PublicKey.fromPem(...)</code>.</p>
 
     <h2 id="porting">Porting to a new language</h2>
     <p>The wire format is small enough to port in an afternoon. The order is:</p>