fix(doctor): recognize embedded bd Dolt JSON output

[onliner10]

Summary

This fixes doctor.bd-dolt / autocodex harness preflight --strict compatibility with newer Beads (bd) embedded Dolt JSON output.

Issue

With bd version 1.0.3, a healthy embedded Dolt workspace can report:

{
  "backend": "dolt",
  "data_dir": "/path/to/.beads/embeddeddolt",
  "database": "weather_agent",
  "embedded": true,
  "schema_version": 1
}

Autocodex currently expects bd dolt show --json to expose an explicit mode field, for example:

{
  "backend": "dolt",
  "mode": "embedded"
}

When mode is absent, the doctor cannot determine Dolt mode and strict harness preflight reports:

doctor.bd-dolt ERROR backend=dolt database=weather_agent (unable to determine dolt mode)

Root Cause

assessBDDoltShowJSON only treats embedded Dolt as healthy when mode == "embedded".

Current Beads embedded-mode JSON may encode the same state as embedded: true without a mode field. The text/status/context commands still identify embedded mode, but the JSON parser path used by Autocodex does not infer mode from that boolean.

Fix

• Read the embedded boolean from bd dolt show --json.
• Treat JSON with no mode and embedded: true as embedded mode.
• Include inferred mode=embedded in the summarized doctor details so preflight output remains clear.
• Add regression coverage for the embedded: true / no mode JSON shape.

After this change, the same healthy workspace is reported as:

doctor.bd-dolt OK backend=dolt mode=embedded database=weather_agent (embedded mode)

Verification

Ran:

go test ./cmd/autocodex -run TestAssessBDDoltShowOutput
go test ./...

Also verified the patched binary against the original failing workspace with:

autocodex harness preflight --strict

Contributing Checklist

Followed CONTRIBUTING.md:

• Fork-based branch: onliner10:fix-bd-embedded-json-mode
• Small scoped change in doctor/preflight parsing only
• Conventional commit: fix(doctor): recognize embedded bd Dolt JSON output
• Behavior change includes regression test coverage
• gofmt applied to touched Go files
• go test ./... passes
• No docs update needed because this is compatibility behavior for an existing doctor check, not a new workflow