Mark 0.2.108 in the changelog and validate submit_result with arktype

[TheGreatAxios]

Two changes, both prerequisites for cutting 0.2.108.

1. Changelog. Renames ## [Unreleased] to ## [0.2.108] - 2026-08-24; the release script requires a clean working tree.

2. Drops the ajv dependency #602 added. arktype is already this repo's validator. It was not a drop-in for #602's design because arktype/@ark/schema only exposes toJsonSchema — the export direction — with no fromJsonSchema, so it cannot validate against a JSON Schema document. The fix is to declare the contract as an arktype type rather than as JSON Schema data:

• ReportContract.outputSchema (JSON Schema object) → outputType?: OutputType (arktype Type)
• RunSubAgentParams.reportSchema → reportType
• submit-result.ts validates via input.outputType(input.result) and instanceof ArkErrors, using .summary for the correction message

Upsides beyond removing a dependency: compile-time types for declared contracts, and better correction text for the worker — verdict must be \"fail\" or \"pass\" (was \"maybe\"), one line per violation, versus ajv.errorsText. Constraints are also terser: score: "0<=number<=10" replaces separate minimum/maximum keys.

No director package had declared an outputSchema yet, so this changes no contract anyone had adopted. bun install reports 1 package removed.

0.2.108 contents, all already merged

• spawn_agent / wait_agents split out of task() (CL-6942: split spawn_agent / wait_agents out of task() #600)
• Fleet authority tiers runtime-enforced (Define the subagents package and its three-tier tool surface #594)
• Retry recovery no longer multiplies with the harness's own retries (Stop retry amplification: director no longer re-wraps harness-exhausted retries #595)
• read_agent_trace for orchestrator tiers (Add read_agent_trace fleet verb (orchestrator tiers only) #599)
• submit_result typed reporting channel for leaves (Add submit_result typed reporting channel for Tier 3 leaves #602, amended here)
• Quoting/backslash no longer bypasses auto-mode shell rules (Fix auto-mode allowing quoted shell redirect writes and dangerous flags #601)
• Interrupt-then-startup crash fixed (Fix startup crash when a stuck workdir lock survives an interrupt #596)
• Approval overlay no longer pushed off screen on short terminals (Fix approval overlay pushing the prompt box off screen on short terminals #597)