dashboard: build-log side-panel viewer in agent card (#726 phase 3)

Adds a `↳ build logs · {agent}` drill-in to every agent card that
opens the side panel and fetches the last 10 build-log headers from
GET /api/build-logs/{agent}. Each row shows a status chip (ok/fail/
running), kind, age, and truncated cmdline. Clicking a row lazily
fetches the full stdout+stderr from GET /api/build-logs/id/{id} and
expands it inline as a scrollable pre.

CSS additions: .build-logs-{panel,toolbar,list,item,row-btn,...} plus
.badge-ok/.badge-fail/.badge-running status chips shared with future
uses. docs/web-ui.md updated with the new drill-in and the new badge
classes.

docs/web-ui/dashboard.md

@@ -369,6 +369,15 @@ fetch entirely.
     layout so the `<pre>` log surface fills the full remaining panel
     height; scroll happens inside the `<pre>`, not the side
     panel body.
+  - `↳ build logs · <agent>` — opens the side panel and fetches
+    the last 10 build-log headers via
+    `GET /api/build-logs/{agent}` (status chip + kind + age +
+    truncated cmdline per row). Clicking a row lazy-fetches its
+    full stdout+stderr from `GET /api/build-logs/id/{id}` and
+    expands it inline as a scrollable `<pre>`. A refresh button
+    re-fetches the header list. Backed by the `build_logs.sqlite`
+    store that `lifecycle::run` and `lifecycle::prebuild_toplevel`
+    write into.
   - Plain navigation links (config repo, forge profile,
     `dashboardLinks` extras) now live in the icon-only nav strip
     on Line 1 — see above. The agent's `config` link