Fix Terraform registry overview: project info + accessflow.bablsoft.com backlink

[babltiga]

Problem

The provider page at https://registry.terraform.io/providers/bablsoft/accessflow/latest (Overview tab and the docs landing page — the registry renders docs/index.md for both) shows the bare tfplugindocs-generated default with no project description and no link back to https://accessflow.bablsoft.com.

Root cause: the hand-written overview in terraform-provider/docs/index.md used tfplugindocs template syntax ({{tffile}}, {{ .SchemaMarkdown }}) but lived in docs/ instead of templates/, so make docs treated it as disposable output and overwrote it. The terraform-provider-v0.5.4 tag was cut from an out-of-band commit (d5c81f53, never merged to main) carrying that regenerated output — which is what the registry published.

Fix

• Move the overview to terraform-provider/templates/index.md.tmpl, where tfplugindocs actually reads it, and expand it with an About AccessFlow section: what the project is, key capabilities, and backlinks to accessflow.bablsoft.com and the GitHub repo.
• Regenerate and commit docs/ on main (verified: the per-resource pages are byte-identical to the v0.5.4 tag's; only index.md changes). tfplugindocs validate passes.
• Update the docs/16-iac.md runbook + GNUmakefile comment so the overview is only ever edited via the template and docs are committed on main before tagging — never as a tag-only commit.

After merge

Publishing requires a new release: push a terraform-provider-v0.5.5 tag so the registry ingests the updated docs/index.md (the registry only re-reads docs on a new version).