fix: wrap up Axum field-test regressions

[gODtECH-Ctl-Create]

Summary

Closes the Rust/Axum v0.2.6 field-test session with only the benchmark-backed fixes included.

Fixed now

• synchronize existing .stackpilot.toml after successful explicit cloud/Terraform remediation so adopted metadata no longer remains cloud = "None" / terraform = false;
• make Terraform provider-variable descriptions identity-neutral so an adopted repo does not surface an unrelated Cargo/application package name;
• document the completed Windows Rust/Axum field test and its validated 100/100 readiness-v1 path.

Explicitly deferred

Follow-up work is tracked in #47: context-aware doctor, readiness-v2 weighting/semantics, safe existing-workflow permission remediation, and the next TypeScript/NestJS adoption benchmark.

Field-test evidence

The benchmark validated installer behavior, inspect/fix preview/apply, idempotency, security baseline generation/detection, explicit workflow permissions, AWS Terraform generation, and successful terraform fmt -check, terraform init, and terraform validate.

No unrelated product expansion is included in this PR.