feat(tui): subagent spawn observability overlay

Adds a live + post-hoc audit surface for recursive delegate_task fan-out.
None of cc/oc/oclaw tackle nested subagent trees inside an Ink overlay;
this ships a view-switched dashboard that handles arbitrary depth + width.

Python
- delegate_tool: every subagent event now carries subagent_id, parent_id,
  depth, model, tool_count; subagent.complete also ships input/output/
  reasoning tokens, cost, api_calls, files_read/files_written, and a
  tail of tool-call outputs
- delegate_tool: new subagent.spawn_requested event + _active_subagents
  registry so the overlay can kill a branch by id and pause new spawns
- tui_gateway: new RPCs delegation.status, delegation.pause,
  subagent.interrupt, spawn_tree.save/list/load (disk under
  \$HERMES_HOME/spawn-trees/<session>/<ts>.json)

TUI
- /agents overlay: full-width list mode (gantt strip + row picker) and
  Enter-to-drill full-width scrollable detail mode; inverse+amber
  selection, heat-coloured branch markers, wall-clock gantt with tick
  ruler, per-branch rollups
- Detail pane: collapsible accordions (Budget, Files, Tool calls, Output,
  Progress, Summary); open-state persists across agents + mode switches
  via a shared atom
- /replay [N|last|list|load <path>] for in-memory + disk history;
  /replay-diff <a> <b> for side-by-side tree comparison
- Status-bar SpawnHud warns as depth/concurrency approaches caps;
  overlay auto-follows the just-finished turn onto history[1]
- Theme: bump DARK dim #B8860B → #CC9B1F for readable secondary text
  globally; keep LIGHT untouched

Tests: +29 new subagentTree unit tests; 215/215 passing.

ui-tui/src/app/useInputHandlers.ts

@@ -74,6 +74,10 @@ export function useInputHandlers(ctx: InputHandlerContext): InputHandlerResult {
     if (overlay.picker) {
       return patchOverlayState({ picker: false })
     }
+
+    if (overlay.agents) {
+      return patchOverlayState({ agents: false })
+    }
   }
 
   const cycleQueue = (dir: 1 | -1) => {
@@ -180,6 +184,7 @@ export function useInputHandlers(ctx: InputHandlerContext): InputHandlerResult {
         if (isCtrl(key, ch, 'c')) {
           cancelOverlayFromCtrlC()
         }
+
         return
       }
 
@@ -290,6 +295,7 @@ export function useInputHandlers(ctx: InputHandlerContext): InputHandlerResult {
     if (key.upArrow && !cState.inputBuf.length) {
       const inputSel = getInputSelection()
       const cursor = inputSel && inputSel.start === inputSel.end ? inputSel.start : null
+
       const noLineAbove =
         !cState.input || (cursor !== null && cState.input.lastIndexOf('\n', Math.max(0, cursor - 1)) < 0)