awf v0.5.0

A minor release adding the Contract-v1 machine-contract stability policy and
richer live visibility for the openai/codex-live agent adapter.

Added

• Machine-contract stability policy (COMPATIBILITY.md):
  the awf run / awf outputs interface, the exit codes, and the workflow format
  plus a published JSON Schema (schema/workflow.v1.schema.json) are now a
  versioned Contract v1, decoupled from the binary's 0.x version. Adds a
  consolidated output-binding-rules section to awf-workflow(5) and a
  COMPATIBILITY section to awf(1).
• Live event visibility for openai/codex-live. The adapter now maps its
  app-server events onto the shared display vocabulary instead of the raw
  [kind] {json} fallback, and fills the previously-empty durable per-event
  journal record: assistant answers stream as prose, reasoning renders dimmed,
  shell commands surface as tool call/result lines (command, elided output,
  line/byte counts, exit status), and a failed turn surfaces a live error. A
  streamed answer that also arrives as a completed item no longer prints twice.

Fixed

• openai/codex-live misread every successful app-server response as an
  error. A nil *RPCError was copied into the error-typed response field,
  producing a non-nil (typed-nil) interface, so each successful JSON-RPC call
  returned a bogus "<nil>" error and turn/start could nil-panic — the
  adapter could not complete a turn. Success responses now carry a true nil
  error.