[P2] ci-cd: provision-service-infra backend initialization failure

## Problem
`provision-service-infra` matrix jobs fail in azd-deploy with Terraform backend initialization errors.

## Evidence
- Run: https://github.com/Azure-Samples/tutor/actions/runs/23241035241
- Failing jobs: all `provision-service-infra (*)`
- Representative log error:
- Error: Backend initialization required, please run "terraform init"
- Reason: Initial configuration of requested backend "azurerm"

## Reproduction
1. Trigger `.github/workflows/azd-deploy.yml` with `release_tier=dev` and `azure_env_name_override=108dev`.
2. Wait for `provision-service-infra` matrix.
3. Observe backend initialization failures in step `Apply changed service-edge stack`.

## Impact
- User impact: High (pipeline fails despite successful foundation + backend deploy).
- Blast radius: CI/CD release path for infra reconciliation and APIM policy drift remediation.

## Acceptance Criteria
- [ ] `provision-service-infra` succeeds for all matrix services in 108dev.
- [ ] Terraform backend strategy is consistent with state/import operations used in job.
- [ ] If backendless mode is chosen, no state/import commands depend on azurerm backend.
- [ ] Full azd-deploy workflow completes successfully in dev (including post-deploy-guardrails).