docs: document configurable lane setups

[joryirving]

Parent: #381

Goal

Document how to configure Dispatch lanes for different deployment shapes.

Requirements

Document at least three supported configurations:

Current default

lanes:
  - id: normal
    title: Normal
    claimable: true
  - id: escalated
    title: Escalated
    claimable: true
  - id: backlog
    title: Backlog
    claimable: false

Single claimable lane

lanes:
  - id: default
    title: Default
    claimable: true
  - id: backlog
    title: Backlog
    claimable: false

Three claimable lanes

lanes:
  - id: local
    title: Local
    claimable: true
  - id: cloud
    title: Cloud
    claimable: true
  - id: frontier
    title: Frontier
    claimable: true
  - id: backlog
    title: Backlog
    claimable: false

These examples are illustrative. Users should be able to pick their own lane IDs.

Documentation topics

• What lanes are.
• Difference between status labels and lanes.
• Difference between claimable and non-claimable lanes.
• How queue APIs use lane.
• How reconciliation/classification assigns lanes.
• How to run a single-lane Dispatch install.
• How to migrate existing lane values safely.
• How to avoid hiding issues with stale/unconfigured lane values.

Non-goals

• Do not document external workflow repo changes.
• Do not require specific model/provider/agent names.
• Do not suggest destructive data rewrites.

Acceptance criteria

• Documentation explains default and custom lanes.
• Documentation includes single-lane and multi-lane examples.
• Documentation warns that status labels are not lane labels.
• Documentation explains non-claimable backlog/intake behavior.
• Documentation links to the relevant queue/reconciliation behavior.

Validation

• npm run lint
• npm run typecheck
• npm run test
• npm run build