fix: regen feature stage docs from HEAD & enforce generation (#26528)

Generate the experimental and beta tables in
docs/install/releases/feature-stages.md from the current source tree
instead of release tags + GitHub API because we found the table of beta
features was stale in recent release(s). This approach works now that
Coder publishes per-release docs.

This change was assisted by Coder Agents.

Makefile

@@ -967,6 +967,7 @@ GEN_FILES := \
 	docs/admin/integrations/prometheus.md \
 	docs/reference/cli/index.md \
 	docs/admin/security/audit-logs.md \
+	docs/install/releases/feature-stages.md \
 	coderd/apidoc/swagger.json \
 	docs/manifest.json \
 	provisioner/terraform/testdata/version \
@@ -1044,6 +1045,7 @@ gen/mark-fresh:
 		docs/admin/integrations/prometheus.md \
 		docs/reference/cli/index.md \
 		docs/admin/security/audit-logs.md \
+		docs/install/releases/feature-stages.md \
 		coderd/apidoc/swagger.json \
 		docs/manifest.json \
 		site/e2e/provisionerGenerated.ts \
@@ -1279,6 +1281,17 @@ docs/admin/security/audit-logs.md: node_modules/.installed coderd/database/queri
 		pnpm exec markdown-table-formatter "$$tmpfile" && \
 		mv "$$tmpfile" "$@" && rm -rf "$$tmpdir"
 
+docs/install/releases/feature-stages.md: \
+	node_modules/.installed \
+	scripts/release/docs_update_feature_stages.sh \
+	codersdk/deployment.go \
+	docs/manifest.json | _gen
+	tmpdir=$$(mktemp -d -p _gen) && tmpfile=$$(realpath "$$tmpdir")/$(notdir $@) && cp "$@" "$$tmpfile" && \
+		./scripts/release/docs_update_feature_stages.sh "$$tmpfile" && \
+		pnpm exec markdownlint-cli2 --fix "$$tmpfile" && \
+		pnpm exec markdown-table-formatter "$$tmpfile" && \
+		mv "$$tmpfile" "$@" && rm -rf "$$tmpdir"
+
 coderd/apidoc/.gen: \
 	node_modules/.installed \
 	scripts/apidocgen/node_modules/.installed \