feat(dashboard): edit in place over the live dashboard with a bottom widget drawer

Milestone 72 phase D — the dashboard view IS the edit surface (operator ask):
- /d/<id> renders the grid via Gridstack in STATIC mode — positioned exactly like
  before, live HTMX widget bodies keep polling. An "Edit" button flips the same
  grid interactive (grid.setStatic(false)) in place, so you drag/resize over real
  data. "Done" flips it back. Layout autosaves on change.
- The widget picker is now a bottom drawer (position:fixed overlay) revealed by
  body.dash-editing — so the dashboard width is identical entering/leaving edit.
- Add: POST returns a single grid item; JS inserts it + grid.makeWidget +
  htmx.process so it loads live data. Remove: POST 204 + grid.removeWidget.
  Per-panel drag handle + remove ✕ are in the DOM for editors, shown only while
  editing.
- Gridstack loads for everyone (viewers get the static grid); edit wiring is
  gated on can_edit. Mobile collapses to one column.
- Removed the separate /d/<id>/edit route + edit.html + _edit_panels.html
  (rule 22). Dashboard-list Edit and new-dashboard create now deep-link
  /d/<id>?edit=1 which opens edit mode on load.

Browser-only behaviour — CI can't exercise it; needs an operator visual check.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/templates/dashboard/_widget_drawer.html

@@ -0,0 +1,78 @@
+{# Bottom drawer — the widget picker, revealed by body.dash-editing. Fixed-position
+   overlay so it never changes the dashboard's width. Add forms are submitted via
+   JS (see index.html) which inserts the returned grid item in place. #}
+<div class="widget-drawer" id="widget-drawer" aria-label="Add a widget">
+  <div style="display:flex;justify-content:space-between;align-items:center;margin-bottom:0.75rem;
+              position:sticky;top:0;background:var(--bg-card);padding-bottom:0.5rem;">
+    <div class="section-title" style="margin-bottom:0;">Add a widget</div>
+    <button type="button" class="btn btn-sm" id="dash-edit-done">Done</button>
+  </div>
+  {% if addable %}
+  {% set _groups = [("core", "Core monitors"), ("capability", "Monitoring capabilities"), ("integration", "Integrations")] %}
+  {% for _gkey, _glabel in _groups %}
+  {% set _gw = addable | selectattr("group", "equalto", _gkey) | list %}
+  {% if _gw %}
+  <div style="font-size:0.72rem;text-transform:uppercase;letter-spacing:0.04em;color:var(--text-dim);margin:0.6rem 0 0.35rem;">{{ _glabel }}</div>
+  <div style="display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:0.5rem;">
+    {% for w in _gw %}
+    <div class="card" style="margin-bottom:0;padding:0;overflow:hidden;">
+      <details>
+        <summary style="display:flex;align-items:center;justify-content:space-between;gap:0.6rem;
+                        padding:0.7rem 0.85rem;cursor:pointer;list-style:none;user-select:none;">
+          <div style="flex:1;min-width:0;">
+            <div style="font-weight:600;font-size:0.85rem;">{{ w.label }}</div>
+            <div style="font-size:0.74rem;color:var(--text-muted);margin-top:0.1rem;">{{ w.description }}</div>
+          </div>
+          <span class="btn btn-sm" style="flex-shrink:0;pointer-events:none;">Add ▾</span>
+        </summary>
+        <form action="/d/{{ dashboard.id }}/edit/add/{{ w.key }}" method="post"
+              class="add-widget-form"
+              style="padding:0.75rem 0.85rem;padding-top:0;border-top:1px solid var(--border);">
+          <div style="display:grid;gap:0.5rem;padding-top:0.75rem;">
+            <div>
+              <label style="font-size:0.74rem;color:var(--text-muted);display:block;margin-bottom:0.2rem;">
+                Widget title <span style="color:var(--text-dim);">(optional)</span>
+              </label>
+              <input type="text" name="title" placeholder="{{ w.label }}"
+                     style="width:100%;padding:0.32rem 0.6rem;background:var(--bg);
+                            border:1px solid var(--border-mid);border-radius:4px;
+                            color:var(--text);font-size:0.85rem;">
+            </div>
+            {% for p in w.params %}
+            <div>
+              <label style="font-size:0.74rem;color:var(--text-muted);display:block;margin-bottom:0.2rem;">{{ p.label }}</label>
+              {% if p.type == "select" %}
+              <select name="param_{{ p.key }}"
+                      style="width:100%;padding:0.32rem 0.6rem;background:var(--bg);
+                             border:1px solid var(--border-mid);border-radius:4px;color:var(--text);font-size:0.85rem;">
+                {% for opt in p.options %}
+                <option value="{{ opt.value }}" {% if opt.value == p.default %}selected{% endif %}>{{ opt.label }}</option>
+                {% endfor %}
+              </select>
+              {% elif p.type == "host" %}
+              <select name="param_{{ p.key }}" required
+                      style="width:100%;padding:0.32rem 0.6rem;background:var(--bg);
+                             border:1px solid var(--border-mid);border-radius:4px;color:var(--text);font-size:0.85rem;">
+                <option value="">— select a host —</option>
+                {% for h in hosts %}
+                <option value="{{ h.id }}">{{ h.name }}</option>
+                {% endfor %}
+              </select>
+              {% endif %}
+            </div>
+            {% endfor %}
+            <button type="submit" class="btn btn-sm" style="width:100%;margin-top:0.1rem;">Add to dashboard</button>
+          </div>
+        </form>
+      </details>
+    </div>
+    {% endfor %}
+  </div>
+  {% endif %}
+  {% endfor %}
+  {% else %}
+  <div style="color:var(--text-muted);font-size:0.85rem;padding:0.5rem 0;">
+    No plugin widgets available. Enable plugins in Settings → Plugins.
+  </div>
+  {% endif %}
+</div>