Product repository template

Layout, proplan.toml, README/CHANGELOG, placeholder product image, .gitignore, KiBot/release/docgen workflows and TEMPLATE.md. Source of truth: contrib/product-template in B4L/proplan (cargo test --test product_template checks it as Gitea 1.27 creates a repository from it).

.gitea/template

@@ -0,0 +1,9 @@
+# Files Gitea fills in when a repository is created from this template: the
+# new repository's name and description go into their text and their path
+# (the board folder under hardware/ is renamed to the repository's name).
+# Gitea 1.27: plain globs only. Everything else (workflows, TEMPLATE.md) is
+# copied as it is.
+proplan.toml
+README.md
+CHANGELOG.md
+hardware/*/README.md