chore(#1055): address argus review nits

- rename cap-cap-col → cap-col; add CSS rules for .cap-col and .cap-save-col
- drop zero-width-space replace in capability header cells (nowrap makes it a no-op)
- add Capability::ALL to hive-sh4re; validate incoming cap strings in post_capabilities

frontend/packages/dashboard/src/dashboard.css

@@ -2077,6 +2077,12 @@ body.logs-shell {
   text-align: left !important;
   min-width: 8em;
 }
+.cap-col {
+  min-width: 5em;
+}
+.cap-save-col {
+  min-width: 4em;
+}
 .cap-agent-name {
   color: var(--fg);
   font-weight: 600;