fix(989): correct four live build-log viewer bugs in logs.js

- live detection: use !h.status (null while running) not === 'running'
- SSE: replace named addEventListener('chunk'/'done') with onmessage +
  frame.done check — backend sends generic message events, no named type
- SSE payload: use frame.stdout_append/stderr_append not frame.text
- timestamps: started_at/finished_at are unix seconds, multiply by 1000
  was already done implicitly — actually use unix arithmetic directly
  to avoid new Date() confusion entirely

Also move the misplaced .flow-main-slim rule from the logs section to
the flow-shell section of dashboard.css.

frontend/packages/dashboard/src/dashboard.css

@@ -1805,6 +1805,11 @@ body.flow-shell .tabbar .tab.active.tab-link {
   bottom: 0;
   overflow: hidden;
 }
+/* flow.html now has a slim header (back link only) instead of the full
+   tabbar — reduce the top padding to match the smaller header height. */
+body.flow-shell .flow-main-slim {
+  padding-top: calc(var(--flow-header-h) + 0.4em);
+}
 .flow-main .terminal-wrap {
   position: absolute;
   inset: 0;
@@ -1864,9 +1869,6 @@ body.logs-shell {
   margin: 0;
   padding: 0;
 }
-body.flow-shell .flow-main-slim {
-  padding-top: calc(var(--flow-header-h) + 0.4em);
-}
 
 .logs-header {
   position: sticky;