feat(#1082): add description() to ToolGroup + Capability; expose in API + UI tooltips

- hive-sh4re: ToolGroup::description() and Capability::description() return
  short human-readable strings for each variant
- hive-c0re: ToolGroupsSnapshot and CapabilitiesSnapshot now include a
  `descriptions` map (name → description); get_capabilities now iterates
  Capability::ALL instead of hardcoding the list
- tabs.js: renderToolGroups + renderCapabilities use descriptions[name] as
  the column header title attribute (native browser tooltip on hover)

frontend/packages/dashboard/src/tabs.js

@@ -1196,7 +1196,7 @@ window.marked = marked;
 
   function renderCapabilities(root, data) {
     root.replaceChildren();
-    const { caps, assignments } = data;
+    const { caps, descriptions = {}, assignments } = data;
     if (!caps || !caps.length) {
       root.append(el('p', { class: 'meta' }, '(no capabilities defined)'));
       return;
@@ -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-col', title: c }, c));
+      hrow.append(el('th', { class: 'cap-col', title: descriptions[c] || c }, c));
     }
     hrow.append(el('th', { class: 'cap-save-col' }, ''));
     thead.append(hrow);
@@ -1311,7 +1311,7 @@ window.marked = marked;
 
   function renderToolGroups(root, data) {
     root.replaceChildren();
-    const { groups, assignments } = data;
+    const { groups, descriptions = {}, assignments } = data;
     if (!groups || !groups.length) {
       root.append(el('p', { class: 'meta' }, '(no tool groups defined)'));
       return;
@@ -1337,7 +1337,7 @@ window.marked = marked;
     const hrow = el('tr');
     hrow.append(el('th', { class: 'tg-agent-col' }, 'agent'));
     for (const g of groups) {
-      hrow.append(el('th', { class: 'tg-group-col', title: g }, g));
+      hrow.append(el('th', { class: 'tg-group-col', title: descriptions[g] || g }, g));
     }
     hrow.append(el('th', { class: 'tg-save-col' }, ''));
     thead.append(hrow);

hive-c0re/src/dashboard.rs

@@ -2512,6 +2512,8 @@ struct ToolGroupsSnapshot {
     /// Ordered list of all known tool-group names. Drives the column
     /// headers in the capabilities table — the UI does not hard-code them.
     groups: Vec<&'static str>,
+    /// Short description for each group name. Keys match `groups` entries.
+    descriptions: std::collections::BTreeMap<&'static str, &'static str>,
     /// Per-agent assignment map. Absent agents use the role default
     /// (agents: messaging+meta+inbox+execution; manager: all groups).
     assignments: std::collections::BTreeMap<String, Vec<String>>,
@@ -2522,9 +2524,14 @@ async fn get_tool_groups(State(_state): State<AppState>) -> axum::Json<ToolGroup
         .iter()
         .map(|g| g.as_str())
         .collect();
+    let descriptions = hive_sh4re::ToolGroup::ALL
+        .iter()
+        .map(|g| (g.as_str(), g.description()))
+        .collect();
     let assignments = crate::tool_groups::read();
     axum::Json(ToolGroupsSnapshot {
         groups,
+        descriptions,
         assignments,
     })
 }
@@ -2566,14 +2573,25 @@ struct CapabilitiesSnapshot {
     /// Ordered list of all known capability names. Drives the column
     /// headers in the capabilities table — the UI does not hard-code them.
     caps: Vec<&'static str>,
+    /// Short description for each capability name. Keys match `caps` entries.
+    descriptions: std::collections::BTreeMap<&'static str, &'static str>,
     /// Per-agent capability grant map. Absent agents have no extra caps.
     assignments: std::collections::BTreeMap<String, Vec<String>>,
 }
 
 async fn get_capabilities(State(_state): State<AppState>) -> axum::Json<CapabilitiesSnapshot> {
-    let caps = hive_sh4re::Capability::ALL.iter().map(|c| c.as_str()).collect();
+    use hive_sh4re::Capability;
+    let caps = Capability::ALL.iter().map(|c| c.as_str()).collect();
+    let descriptions = Capability::ALL
+        .iter()
+        .map(|c| (c.as_str(), c.description()))
+        .collect();
     let assignments = crate::capabilities::read();
-    axum::Json(CapabilitiesSnapshot { caps, assignments })
+    axum::Json(CapabilitiesSnapshot {
+        caps,
+        descriptions,
+        assignments,
+    })
 }
 
 #[derive(Deserialize)]

hive-sh4re/src/lib.rs

@@ -876,6 +876,30 @@ impl ToolGroup {
             Self::WebTools => "web_tools",
         }
     }
+
+    /// Short human-readable description suitable for a tooltip or help text.
+    #[must_use]
+    pub fn description(self) -> &'static str {
+        match self {
+            Self::Messaging => "send, recv, ask, answer — core agent communication",
+            Self::Meta => "set_status, get_agent_meta — identity and status",
+            Self::Inbox => {
+                "get_loose_ends, cancel_loose_end, remind, request_next_turn — self-scheduling"
+            }
+            Self::Lifecycle => "kill, start, restart, update — container lifecycle (privileged)",
+            Self::Approvals => {
+                "request_init_config, request_apply_commit, request_update_meta_inputs — config change flow (privileged)"
+            }
+            Self::Scheduling => {
+                "request_schedule_prompt and related — operator-visible scheduled prompts (privileged)"
+            }
+            Self::Diagnostics => "get_logs — read host journal and build logs (privileged)",
+            Self::Execution => "bash_run, bash_status — run shell commands in the container",
+            Self::WebTools => {
+                "WebFetch, WebSearch — Claude built-in web egress; not MCP tools"
+            }
+        }
+    }
 }
 
 /// Per-agent capability grants. Stored in `meta/capabilities.json`
@@ -962,6 +986,20 @@ impl Capability {
             Self::QueryAgentState => "query_agent_state",
         }
     }
+
+    /// Short human-readable description suitable for a tooltip or help text.
+    #[must_use]
+    pub fn description(self) -> &'static str {
+        match self {
+            Self::ManageRootAgent => {
+                "lifecycle-manage the root/manager agent on hive crash recovery"
+            }
+            Self::ReadHostJournal => "read host journald via get_host_journal MCP tool",
+            Self::QueryAgentState => {
+                "query non-child agents' loose ends and reminder state via get_loose_ends"
+            }
+        }
+    }
 }
 
 /// Schedule row shape on the wire — mirror of