feat: add cost and usage tracking to output directory per step and overall task

[ereslibre]

Add usage and cost tracking throughout the task lifecycle. Each iteration now records its usage (tokens, cost, model, agent) in iteration.json, and the task description aggregates usage across all iterations. The inspect command displays a new Usage section, and the list command syncs usage on every refresh.

Changes

Schemas (packages/schemas)

• Added UsageReportSchema and StepUsageReportSchema Zod schemas in packages/schemas/src/usage/schema.ts
• UsageReport and StepUsageReport types are now inferred from Zod schemas (z.infer<typeof ...>) instead of manually defined interfaces
• Bumped IterationSchema to v1.2 with an optional usage field
• Bumped TaskDescriptionSchema to v1.6 with an optional usage field
• Exported UsageReportSchema, StepUsageReportSchema, and StepUsageReport from the package index

Core (packages/core)

• IterationManager gains usage getter and setUsage() method; added migration from v1.1 → v1.2
• TaskDescriptionManager.updateStatusFromIteration() now catches missing status.json gracefully and calls syncUsage() on terminal states
• Added TaskDescriptionManager.syncUsage() that rebuilds task-level usage by summing iteration data via accumulateUsage()
• Added usage getter to TaskDescriptionManager
• Added private accumulateUsage() helper that sums two UsageReport values, resolving agent/model only when all reports agree
• aggregateUsage in WorkflowManager now builds a per-step StepUsageReport[] breakdown and resolves top-level agent/model only when all steps agree
• UsageTracker now tracks agent alongside model, with the same single-value-when-unanimous resolution strategy

Agent (packages/agent)

• runCommand persists workflowUsage to iteration.json via IterationManager.setUsage()
• ACP runner attaches agent (tool name) to usage reports alongside model
• run command displays Agent in usage properties output

CLI (packages/cli)

• inspect command calls task.updateStatusFromIteration() before display, includes usage in output, and renders a new Usage section (cost, input/output/total tokens)
• list command comment updated to reflect usage sync on terminal states
• Added usage field to TaskInspectionOutput interface

Notes

• The task description schema version was bumped from 1.5 to 1.6; iteration schema from 1.1 to 1.2.
• Top-level agent and model on aggregated reports are intentionally set only when all contributing steps/iterations used the same value; otherwise they are left undefined.
• Usage is persisted only in iteration.json (versioned); status.json is not modified with cost data.

[Angelmmiguel]

LGTM! Amazing we are reporting and storing all this data. This is mandatory for autonomous systems 😄