Fix README diagram: needs-clarification revisits the named earlier stage

Addresses review 4724027270 on PR #3568. The overview flowchart routed every
needs-clarification verdict back to research, but decide.md's Revisit stage can
send an idea back to intake, research, define, or shape. Reroute the arrow as a
generic loop back to the earlier stages so the diagram no longer misstates the
pipeline.

Assisted-by: GitHub Copilot (model: Claude Opus 4.8, supervised)
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 1f25cf9d-b7eb-4b2b-b811-3e91d8db8f6a

Author: mnriem

extensions/assess/README.md

@@ -23,8 +23,8 @@ The pipeline is a **funnel**: most ideas should be killed or parked before `shap
 flowchart LR
     A[intake] --> R[research] --> D[define] --> S[shape] --> C{decide}
     C -->|go| SPEC[/speckit.specify/]
-    C -->|needs-clarification| R
     C -->|kill| X[closed, recorded]
+    C -.->|needs-clarification: revisit the named earlier stage| A
 ```
 
 ## Commands