Focus v0.1 on Datadog migration plans

[RamazanKara]

What changed

• centers the primary CLI on deterministic, read-only Datadog scanning, planning, and export
• inventories Datadog resources and classifies every conversion as exact, approximate, manual, or unsupported
• generates Grafana dashboards, Prometheus alert rules, Alloy/OpenTelemetry configuration, provenance links, a static HTML report, and a transparent exit-readiness score
• moves the existing non-Datadog paths into an experimental-provider surface
• updates release documentation and records the inaugural v0.1.0 release

Why

OpenExit v0.1 needs one trustworthy migration path. This makes Datadog to Grafana LGTM the reviewed, deterministic product surface while preserving other providers as experimental.

Impact

The primary command surface is now:

openexit datadog scan
openexit datadog plan --target grafana-lgtm
openexit datadog export --out migration/

No writes are made to Datadog or target systems, and no AI conversion or automatic deployment is included.

Validation

• make release-check VERSION=v0.1.0
• go test -race ./internal/datadogplan ./internal/app -count=1