docs: add base param + /api/diff/switch to Review Server API table

CLAUDE.md (symlinked to AGENTS.md) was edited in the previous commit
but AGENTS.md wasn't staged. This captures the actual file change.

For provenance purposes, this commit was AI assisted.

Author: backnotprop

AGENTS.md

@@ -223,8 +223,9 @@ During normal plan review, an Archive sidebar tab provides the same browsing via
 
 | Endpoint              | Method | Purpose                                    |
 | --------------------- | ------ | ------------------------------------------ |
-| `/api/diff`           | GET    | Returns `{ rawPatch, gitRef, origin, diffType, gitContext }` |
-| `/api/file-content`   | GET    | Returns `{ oldContent, newContent }` for expandable diff context |
+| `/api/diff`           | GET    | Returns `{ rawPatch, gitRef, origin, diffType, base, gitContext }` |
+| `/api/diff/switch`    | POST   | Switch diff type and/or base branch (body: `{ diffType, base? }`) |
+| `/api/file-content`   | GET    | Returns `{ oldContent, newContent }` for expandable diff context (`?path=&oldPath=&base=`) |
 | `/api/git-add`        | POST   | Stage/unstage a file (body: `{ filePath, undo? }`) |
 | `/api/feedback`       | POST   | Submit review (body: feedback, annotations, agentSwitch) |
 | `/api/image`          | GET    | Serve image by path query param            |