bruno: replace Python generator with Go golden-writer in the drift test

The generator moves into the Go toolchain per repo preference:
internal/docs/bruno_gen.go emits the OpenCollection mirrors (same output
contract — gate-verified example-request bodies, env-var params,
device-token headers, login/register/refresh token-capture scripts) and
TestBrunoMirrorsDocs grows a -update flag: verification by default,
regeneration on demand:

  go test ./internal/docs -run TestBrunoMirrorsDocs -update

Generator and checker are now the same code — they cannot drift apart.
scripts/gen_bruno_from_docs.py deleted; opencollection.yml README points
at the go-test command.

Also fixed vs the Python pass: mirror placement follows the docs tree
folder (RelPath), not the area frontmatter (several docs — highlights,
notes, ratings, users, progress — carry a different area); docs blocks
emit the collection's mapping form (content + type), not a bare scalar;
JSON body sanity is checked at generation time.

Idempotent: back-to-back -update runs are byte-identical.
make test green (9 pkgs).

bruno/authentication/login.yml

@@ -24,28 +24,30 @@ runtime:
   scripts:
     - type: after-response
       code: |-
-          function onResponse(res) {
-            try {
-              const responseBody = res.getBody();
-              const token = responseBody.access_token;
-              const refreshToken = responseBody.refresh_token;
-              if (token) {
-                bru.setEnvVar("token", token, { persist: true });
-                console.log("Access token saved");
-              }
-              if (refreshToken) {
-                bru.setEnvVar("refresh_token", refreshToken, { persist: true });
-                console.log("Refresh token saved");
-              }
-            } catch (error) {
-              console.error("Token capture failed:", error.message);
+        function onResponse(res) {
+          try {
+            const responseBody = res.getBody();
+            const token = responseBody.access_token;
+            const refreshToken = responseBody.refresh_token;
+            if (token) {
+              bru.setEnvVar("token", token, { persist: true });
+              console.log("Access token saved");
             }
+            if (refreshToken) {
+              bru.setEnvVar("refresh_token", refreshToken, { persist: true });
+              console.log("Refresh token saved");
+            }
+          } catch (error) {
+            console.error("Token capture failed:", error.message);
           }
-          onResponse();
+        }
+        onResponse();
 
-docs: |-
-  # Login User
+docs:
+  content: |-
+    # Login User
 
-  `POST /api/auth/login` — auth: none.
+    `POST /api/auth/login` — auth: none.
 
-  Canonical reference: `docs/developer/api/authentication/login.md` (docs site → Developer → API). This request is GENERATED from that doc; edit the doc, not this file.
+    Canonical reference: docs/developer/api/authentication/login.md (docs site → Developer → API). This request is GENERATED from that doc; edit the doc, then run the drift test with -update.
+  type: text/markdown