fix: update nostrcalendar code examples to use new import name

The nostrcalendar package renamed its import from `nostrcal` to
`nostrcalendar` in v0.2.0. Update the two code examples on the
/openclaw page to match.

Author: vveerrgg

docs/openclaw.html

@@ -857,7 +857,7 @@ <h2>Quick Start</h2>
                 <button class="copy-btn" onclick="copyCode('code-nc-quickstart')">Copy</button>
 <span class="kw">import</span> asyncio
 <span class="kw">from</span> nostrkey <span class="kw">import</span> Identity
-<span class="kw">from</span> nostrcal <span class="kw">import</span> (
+<span class="kw">from</span> nostrcalendar <span class="kw">import</span> (
     AvailabilityRule, DayOfWeek, TimeSlot,
     publish_availability, get_free_slots,
 )
@@ -911,7 +911,7 @@ <h2>Agent-to-Agent Negotiation</h2>
             <p class="subtitle">Two agents find mutual free time and book a meeting without human involvement.</p>
             <div class="code-block" id="code-nc-negotiate">
                 <button class="copy-btn" onclick="copyCode('code-nc-negotiate')">Copy</button>
-<span class="kw">from</span> nostrcal <span class="kw">import</span> find_mutual_availability, propose_times
+<span class="kw">from</span> nostrcalendar <span class="kw">import</span> find_mutual_availability, propose_times
 <span class="kw">from</span> datetime <span class="kw">import</span> datetime
 
 <span class="comment"># Find overlapping free slots across multiple days</span>