docs: add 39-branch Keycloak governance index

docs/keycloak-branch-index.md

@@ -0,0 +1,29 @@
+# Keycloak branch implementation index
+
+The source inventory contains 39 `feature-keycloak-*.md` branch notes. This
+repository preserves one local Git feature branch for every note and merges it
+with `--no-ff` into either the common `develop` baseline or one of the four
+authentication-pattern branches.
+
+| Target | Meaning |
+|---|---|
+| `common` | Shared realm, federation, deployment, or governance contract. Merge into `develop`, then propagate to AP1–AP4. |
+| `ap1` | Browser-based OAuth client: vanilla SPA, Authorization Code + PKCE, Resource Server. |
+| `ap2` | Token-mediating confidential backend: browser receives access token only. |
+| `ap3` | BFF: backend owns every OAuth token and browser owns only a session cookie. |
+| `ap4` | Edge forward-auth: oauth2-proxy/Nginx owns login and backend trusts an isolated identity header. |
+
+The machine-readable registry is
+[`keycloak-branch-manifest.tsv`](keycloak-branch-manifest.tsv). Run:
+
+```bash
+./scripts/audit-keycloak-branches.sh
+```
+
+The audit succeeds only when all 39 note names have matching local feature
+branches and each feature tip is reachable from its declared target branch.
+
+Google credentials are never committed. The default local acceptance harness
+uses a second Keycloak realm as a controllable OIDC provider so claim mapping
+and unsafe-linking failure paths can be reproduced. A real Google login remains
+an explicit credentialed/public-HTTPS verification profile.