docs: surface idempotent-by-name + delete lifecycle on /agent (#8)

/agent.html is the page agents parse before they adopt the service —
the "what am I getting into" contract for a CLAUDE.md reader. Two
things it was silent about:

1. POST /db/new is idempotent by name for authenticated callers
   (PR #8 on the API). Previously the page implied each POST was a
   fresh provision; a nightly re-run would look like it leaked
   resources. Now explicit.

2. Delete lifecycle: paid accounts can DELETE on demand, free
   accounts get 24h auto-expiry. No mention of this anywhere on the
   marketing pages before; devs had to sign in to discover the
   model. Surface it in the intro so it factors into the "is this
   right for my workflow" call.

One paragraph added to the intro block. Covers both.

Author: mastermanas805

agent.html

@@ -232,7 +232,8 @@ <h1>Make your agent provision its own database</h1>
 
     <div class="intro">
       <p>Pick the file that matches your tool. Copy it, commit it to your repo, done. The agent reads it before its next turn and uses the single POST below as its default path to a database.</p>
-      <p>The contract is tiny: <code>POST https://api.instanode.dev/db/new</code> with body <code>{"name":"&lt;slug&gt;"}</code> returns a <code>connection_url</code>. pgvector is pre-installed. Anonymous databases live 24 hours; claim them from the dashboard to make them permanent.</p>
+      <p>The contract is tiny: <code>POST https://api.instanode.dev/db/new</code> with body <code>{"name":"&lt;slug&gt;"}</code> returns a <code>connection_url</code>. pgvector is pre-installed. Re-running the same POST with the same name reuses the same database — idempotent by name for signed-in callers, so your script's nightly re-run doesn't leak duplicates.</p>
+      <p>Lifecycle: anonymous databases live 24 hours and auto-expire. Claim from the <a href="/dashboard.html">dashboard</a> to keep them permanent. Paid accounts can drop a resource on demand via <code>DELETE /api/me/resources/{token}</code>; free accounts wait for the 24h auto-expiry.</p>
     </div>
 
     <!-- CLAUDE.md -->