v0.8.2 — backfill logging on schema-mode path

Patch release. v0.8.0 / v0.8.1 left four logging gaps:
parse_json_response was silent, run_with_json_retry had no terminal
summary, oai.chat_completions had no entry/success log, header parse
helpers had no rejection warning.

Backfilled:
  - adapters.base.parse_json_response: DEBUG per candidate,
    DEBUG on winner, INFO summary on all-failed, WARN if jsonschema
    lib missing.
  - shared.runner.run_with_json_retry: INFO on entry, DEBUG per
    attempt, INFO/WARN per retry, INFO terminal summary
    (outcome=success|exhausted|crashed, attempts, retries,
    total_usage).
  - oai.chat_completions: INFO entry (model, stream, msg count,
    flag presence), INFO on schema/non-schema success, header
    parsers WARN on rejected values (truncated ≤80 chars).

Uses the existing project _JsonFormatter — DEBUG=1 → JSON with
ts/level/logger/func/line/file/msg. No new dependency.

No secrets / tokens / bodies / env dumps logged. All 151 existing
tests pass. No behavior change — observability only.

Migration: none — internal change.