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;

frontend/packages/dashboard/src/tabs.js

@@ -1221,7 +1221,7 @@ window.marked = marked;
     const hrow = el('tr');
     hrow.append(el('th', { class: 'cap-agent-col' }, 'agent'));
     for (const c of caps) {
-      hrow.append(el('th', { class: 'cap-cap-col', title: c }, c.replace(/_/g, '_​')));
+      hrow.append(el('th', { class: 'cap-col', title: c }, c));
     }
     hrow.append(el('th', { class: 'cap-save-col' }, ''));
     thead.append(hrow);
@@ -1240,7 +1240,7 @@ window.marked = marked;
       const checkboxes = [];
       for (const c of caps) {
         const checked = assigned.includes(c);
-        const td = el('td', { class: 'cap-cap-col' });
+        const td = el('td', { class: 'cap-col' });
         const cb = el('input', {
           type: 'checkbox',
           class: 'cap-cb',