Embed supervisor schema version in airflow-metadata.yaml for executable bundles #66941

Background

The cross-language protocol compatibility work in #66590 introduces
Cadwyn-based schema migration so the supervisor can talk to lang-SDK
runtimes pinned to older schema versions. Java will declare the schema
version it was built against via a JAR-manifest attribute
(Airflow-SDK-Supervisor-Schema-Version); the equivalent for an
executable bundle is a key in airflow-metadata.yaml.

Today airflow-metadata.yaml (see
providers/sdk/executable/docs/bundle-spec.rst) carries sdk.language
and sdk.version but no schema-version pin.

What needs to happen

1. Add sdk.supervisor_schema_version (or equivalent) to the
   airflow-metadata.yaml schema and the published JSON Schema.
2. Have airflow-go-pack (and any future packer) write the version it
   was built against into the manifest.
3. Have the Python side
   (providers/sdk/executable/src/airflow/providers/sdk/executable/bundle_scanner.py)
   read the field and pass it to the supervisor's CommsDecoder.bind
   call so request/response migration kicks in.
4. Bump bundle-spec format_version minor.

Acceptance criteria

• A bundle built against schema vN keeps working when paired with a
  supervisor on schema vN+1, exercised in tests.
• Missing field is treated as "head version" (current behaviour).

Context

• Cross-SDK protocol versioning: Compatible protocol between coordinator and lang-SDK #66590.
• Java-side TODO under Compatible protocol between coordinator and lang-SDK #66590: "Add Supervisor Schema Version to Java
  SDK JAR manifest".
• Bundle-spec source of truth: providers/sdk/executable/docs/bundle-spec.rst.
• Schema versioning impl (astronomer fork): astronomer/airflow#1577.

Drafted-by: Claude Code (Opus 4.7) (no human review before posting)