dashboard: add toc-sidebar utility; move live indicator into TOC column

Extracts the TOC-injection pattern into a reusable component:

  src/components/toc-sidebar.js
    injectTocTop(id, element) — prepends an element to #observablehq-toc,
    removing any previous instance with the same id first so reactive cells
    can re-inject on each poll without accumulating duplicates.

decisions.md now uses injectTocTop to place a single widget (live
indicator + Decision Health KPI box) into the right-column sidebar,
removing the standalone live-indicator cell and the ad-hoc id/remove
pattern that was previously inlined.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/src/decisions.md

@@ -103,7 +103,8 @@ function fmtDuration(ms) {
 # Decisions
 
 ```js
-import {withDocHelp} from "./components/doc-overlay.js";
+import {withDocHelp}   from "./components/doc-overlay.js";
+import {injectTocTop} from "./components/toc-sidebar.js";
 
 // ── KPI computation (uses full data, not filtered) ──────────────────────────
 const _resolved5 = data
@@ -150,22 +151,16 @@ const _kpiBox = html`<div class="kpi-infobox">
 
 withDocHelp(_kpiBox, "/docs/decisions-kpi");
 
-// ── Inject into the TOC sidebar (right column, non-scrolling) ───────────────
-_kpiBox.id = "decisions-kpi-box";
-const _toc = document.querySelector("#observablehq-toc");
-if (_toc) {
-  document.getElementById("decisions-kpi-box")?.remove();
-  _toc.prepend(_kpiBox);
-} else display(html`<div style="float:right;width:215px;margin-left:1rem">${_kpiBox}</div>`);
-```
-
-```js
-display(html`<div class="live-indicator">
+// ── Build sidebar widget: live indicator + KPI box ──────────────────────────
+const _liveEl = html`<div class="live-indicator">
   <span style="color:${_ok ? 'var(--theme-foreground-focus)' : 'red'}">●</span>
   ${_ok
     ? `Live · updated ${_ts?.toLocaleTimeString()}`
     : html`<span style="color:red">Offline — run: <code>make api</code></span>`}
-</div>`);
+</div>`;
+
+const _tocInjected = injectTocTop("decisions-sidebar", html`<div>${_liveEl}${_kpiBox}</div>`);
+if (!_tocInjected) display(html`<div style="float:right;width:215px;margin-left:1rem">${_liveEl}${_kpiBox}</div>`);
 ```
 
 ## Resolution History