feat(#1098): replace deployed:hash chip with config link in three-dot menu

Remove the deployed sha plain-text badge from the card head.
Add a forge-linked menu item to the three-dot menu instead:
'deployed:abc123def012 ↗' opens agent-configs/<name>/commit/<sha>
on the hive forge in a new tab.

Only shown when both c.deployed_sha and forgeBase are present.
buildAgentMenu now takes forgeBase as second arg; call site passes
the same forgeBase computed for nav-strip links.

CSS: add text-decoration: none + box-sizing to .agent-menu-item
so <a> link items render identically to the <button> items.

frontend/packages/dashboard/src/dashboard.css

@@ -415,6 +415,8 @@ body.dashboard-shell {
   text-align: left;
   padding: 0.4em 0.9em;
   cursor: pointer;
+  text-decoration: none;
+  box-sizing: border-box;
 }
 .agent-menu-item:hover {
   background: var(--border);