fix(workflows): drop the bundled speckit workflow's inert scope input

The bundled workflow declared a required-choice scope input that no step
referenced. All four steps pass {{ inputs.spec }}, so every choice behaved
identically.

The value was enum-validated and then discarded, which is worse than being
ignored outright: -i scope=bogus errors while -i scope=backend-only is
accepted, so the rejection of an invalid value is evidence to the user that
the flag does something.

Propagating scope instead would need a contract that does not exist -- the
steps take a single args string, so a scope could only be appended as prose
to the user's own description and left to the agent to interpret. That is a
feature with a design question attached, not a bug fix, so this removes the
selector and leaves the door open for a real one.

workflows/README.md demonstrated multiple inputs using this exact input
against the bundled workflow, so that example moves to a declared one.

Every declared input is now referenced and every referenced input declared.

Fixes #4384

Author: Yash-Chindam

workflows/README.md

@@ -73,7 +73,7 @@ specify workflow run ./my-workflow.yml --input spec="Build a user authentication
 ```bash
 specify workflow run speckit \
   --input spec="Build a user authentication system with OAuth support" \
-  --input scope="backend-only"
+  --input integration="claude"
 ```
 
 ## Step Types

workflows/speckit/workflow.yml

@@ -35,10 +35,6 @@ inputs:
     type: string
     default: "auto"
     prompt: "Integration to use (e.g. claude, copilot, gemini; 'auto' uses the project's initialized integration)"
-  scope:
-    type: string
-    default: "full"
-    enum: ["full", "backend-only", "frontend-only"]
 
 steps:
   - id: specify