feat: drawer witness flag inline-edit (T72.3)

Memories grow per-flag witness checkboxes (you / host / guest) that
auto-submit on change via HTMX. The new POST route emits a manual_edit
event with target_kind=memory_witness and a {flag, value} payload;
prior_value mirrors the same shape so an inverse edit restores the
flag. The drawer's recent-memories query now selects the three
witness columns alongside the existing fields so the template can
render checkbox state without a second query per row.

chat/templates/_drawer.html

@@ -347,6 +347,23 @@
               <input type="hidden" name="pinned" value="{{ 0 if m.pinned else 1 }}">
               <button type="submit">{{ 'Unpin' if m.pinned else 'Pin' }}</button>
             </form>
+            <div class="witness-row">
+              {% for flag in ['you', 'host', 'guest'] %}
+                {% set witnessed = m['witness_' ~ flag] %}
+                <form class="inline-edit"
+                      hx-post="/chats/{{ chat.id }}/drawer/memory/witness"
+                      hx-target="#drawer" hx-swap="innerHTML">
+                  <input type="hidden" name="memory_id" value="{{ m.id }}">
+                  <input type="hidden" name="flag" value="{{ flag }}">
+                  <input type="hidden" name="new_value" value="{{ 0 if witnessed else 1 }}">
+                  <label>
+                    <input type="checkbox" {% if witnessed %}checked{% endif %}
+                           onchange="this.form.requestSubmit()">
+                    {{ flag }}
+                  </label>
+                </form>
+              {% endfor %}
+            </div>
             <details>
               <summary>Edit POV summary</summary>
               <form class="inline-edit"