feat(mcp-server): configurable async concurrency controller (#238)

[Neftedollar]

Summary

• replace async global inflight lock with a configurable concurrency controller
• add CLI/programmatic concurrency options (maxConcurrentJobs, maxConcurrentJobsPerWorkflow, workflow-scoped maps)
• preserve sync-path behavior and keep async observer tools non-blocking
• keep async persistence/recovery integration intact after rebasing on P0: Persist async job registry and recover jobs after server restart #237

What changed

• added packages/mcp-server/src/concurrency.ts with validated limits and deterministic BUSY errors
• wired concurrency permits into async dispatchStart (start + job permits with safe release on complete/error)
• extended single-workflow and programmatic APIs to accept concurrency/async settings
• validated programmatic per-workflow concurrency references against known workflow names
• updated CLI parsing/validation/help for concurrency flags
• merged with persistence changes from P0: Persist async job registry and recover jobs after server restart #237 (RunStore + sqlite store path)

Tests

• bun run --filter @ageflow/mcp-server typecheck
• bun run --filter @ageflow/mcp-server test
• bun run --filter @ageflow/cli typecheck
• bun run --filter @ageflow/cli test

Closes #238