Add browser save and update workflow

docs/browser-extension.md

@@ -134,6 +134,31 @@ Expected behavior:
   and turns the locked affordance back into live matches without requiring a
   page reload.
 
+## Save And Update Workflow
+
+User story:
+
+- After the user submits a login form, the browser extension should help store
+  that credential instead of forcing the user back into KeePassGO manually.
+- If KeePassGO already has a matching entry for that site and username, the
+  popup should offer an update.
+- If the user is creating a new login, the popup should let the user save it
+  into a relevant vault group without leaving the browser.
+
+Expected behavior:
+
+- Submitted login forms queue a pending browser save/update state for the
+  active tab.
+- The popup shows that pending save/update state prominently instead of hiding
+  it behind page matches alone.
+- When KeePassGO finds an exact browser match for the submitted username and
+  site, the popup offers an `Update` action for that entry.
+- When there is no exact entry match, the popup offers a `Save` action using a
+  relevant group path from the current page matches or a user-selected search
+  result.
+- The browser save/update action writes through KeePassGO's existing secure
+  gRPC mutation API and stays scoped to the browser token's allowed groups.
+
 For extension-side regression checks, run:
 
 ```bash