feat(#986): dedicated logs page with build/agent/system sub-tabs

Add /logs.html as a standalone page (same back-link pattern as flow.html):
- BUILD tab: all-agents build log history via new GET /api/build-logs endpoint
- AGENT tab: per-container journald viewer with agent selector + unit filter
- SYSTEM tab: host-side hive-c0re.service logs via new GET /api/journal-host endpoint

Remove inline log drill-ins from SW4RM container rows (buildJournalTrigger
and buildBuildLogsTrigger) — log viewing now lives on the dedicated page.

flow.html: strip the full dashboard tabbar, replace with a simple back link
matching the new logs page chrome.

index.html: add L0GS tab link to /logs.html in the tab strip.

Backend additions:
- build_logs::list_recent_all — cross-agent query (newest first, cap 100)
- GET /api/build-logs — all-agents variant backed by list_recent_all
- GET /api/journal-host — host journald (no -M container flag), restricted
  to allow-listed units (hive-c0re.service)

frontend/packages/dashboard/build.mjs

@@ -2,11 +2,14 @@
 //
 //   dist/index.html               served by the Rust router at GET /
 //   dist/flow.html                served at GET /flow.html
+//   dist/logs.html                served at GET /logs.html
 //   dist/static/tabs.js           /index.html entry — tab renderers +
 //                                  tab routing + refreshState
 //   dist/static/flow.js           /flow.html entry — broker terminal +
 //                                  operator inbox + @-mention composer
-//   dist/static/{tabs,flow}.js.map source map siblings
+//   dist/static/logs.js           /logs.html entry — build/agent/system
+//                                  log viewer sub-tabs
+//   dist/static/{tabs,flow,logs}.js.map source map siblings
 //   dist/static/dashboard.css     served at /static/dashboard.css
 //                                  (@import resolved from @hive/shared)
 //
@@ -35,7 +38,7 @@ mkdirSync(staticDir(''), { recursive: true });
 // follow-up once asset sizes warrant it). esbuild writes each entry
 // to `static/<name>.js` based on the entryPoint basename.
 await build({
-  entryPoints: [src('tabs.js'), src('flow.js')],
+  entryPoints: [src('tabs.js'), src('flow.js'), src('logs.js')],
   outdir: staticDir(''),
   bundle: true,
   format: 'esm',
@@ -78,7 +81,7 @@ await build({
   logLevel: 'info',
 });
 
-for (const html of ['index.html', 'flow.html']) {
+for (const html of ['index.html', 'flow.html', 'logs.html']) {
   copyFileSync(src(html), dist(html));
 }