Go v2: preview → GA hardening

[ananth7592]

Part of the Cosmos DB Go SDK v2 (azcosmos/v2) effort, delivering the Go v2 data plane over an FFI/cgo binding to the shared Rust Cosmos driver (decision: Azure/azure-sdk-for-go#27238, ADR docs/adr/0001-go-v2-uses-ffi.md). This ships a supportable GA. Self-contained; owners decide how to complete it.

Scope

• Validate the full Big-5 + musl matrix including Alpine/container smoke tests.
• Cross-compilation guidance.
• Supportability/telemetry playbook spanning Go binding ↔ C ABI ↔ Rust driver.
• Docs, samples, and a v1→v2 migration guide.
• Pinned feedback issue in azure-sdk-for-go.
• Dapr/AKS + User-Agent OS/arch input.
• Rollout and rollback rehearsal.
• (Performance and FFI-robustness baselines are owned by the M11/M10 issues and consumed here as GA gates.)

Deliverables

• GA-quality docs/migration; container-validated matrix; release/rollback rehearsal; preview-feedback burn-down.

Definition of done

• Clean build + sample on every claimed target including Alpine; disabled-cgo / unsupported platform produce intentional documented behavior; migration guide validated; preview feedback resolved.