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/types.ts

@@ -12,16 +12,72 @@ export interface ActivityItem {
 }
 
 export interface SubagentProgress {
+  apiCalls?: number
+  costUsd?: number
+  depth: number
   durationSeconds?: number
+  filesRead?: string[]
+  filesWritten?: string[]
   goal: string
   id: string
   index: number
+  inputTokens?: number
+  iteration?: number
+  model?: string
   notes: string[]
-  status: 'completed' | 'failed' | 'interrupted' | 'running'
+  outputTail?: SubagentOutputEntry[]
+  outputTokens?: number
+  parentId: null | string
+  reasoningTokens?: number
+  startedAt?: number
+  status: 'completed' | 'failed' | 'interrupted' | 'queued' | 'running'
   summary?: string
   taskCount: number
   thinking: string[]
+  toolCount: number
   tools: string[]
+  toolsets?: string[]
+}
+
+export interface SubagentOutputEntry {
+  isError: boolean
+  preview: string
+  tool: string
+}
+
+export interface SubagentNode {
+  aggregate: SubagentAggregate
+  children: SubagentNode[]
+  item: SubagentProgress
+}
+
+export interface SubagentAggregate {
+  activeCount: number
+  costUsd: number
+  descendantCount: number
+  filesTouched: number
+  hotness: number
+  inputTokens: number
+  maxDepthFromHere: number
+  outputTokens: number
+  totalDuration: number
+  totalTools: number
+}
+
+export interface DelegationStatus {
+  active: {
+    depth?: number
+    goal?: string
+    model?: null | string
+    parent_id?: null | string
+    started_at?: number
+    status?: string
+    subagent_id?: string
+    tool_count?: number
+  }[]
+  max_concurrent_children?: number
+  max_spawn_depth?: number
+  paused: boolean
 }
 
 export interface ApprovalReq {