docs: align checklist wording with CLI next-steps phrasing

Address review: state the checklist's purpose (validate requirements completeness, clarity, and consistency) and anchor it to /speckit.plan as the CLI does, use the plural 'quality checklists', and reword the Taskify step so the spec is validated using the generated checklists.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jawwad-ali

docs/quickstart.md

@@ -16,7 +16,7 @@ After installing Spec Kit and defining your project constitution, quick experime
 /speckit.constitution -> /speckit.specify -> /speckit.clarify -> /speckit.plan -> /speckit.checklist -> /speckit.tasks -> /speckit.analyze -> /speckit.implement
 ```
 
-Use `/speckit.clarify` to reduce requirement ambiguity before planning, `/speckit.checklist` to generate quality checklists for the requirements once the plan exists, and `/speckit.analyze` to check spec/plan/task consistency before implementation starts. You can repeat `/speckit.analyze` after implementation as an extra review, but keep the first analysis before `/speckit.implement` so gaps are caught while the plan and tasks can still be adjusted.
+Use `/speckit.clarify` to reduce requirement ambiguity before planning, `/speckit.checklist` (after `/speckit.plan`) to generate quality checklists that validate requirements completeness, clarity, and consistency, and `/speckit.analyze` to check spec/plan/task consistency before implementation starts. You can repeat `/speckit.analyze` after implementation as an extra review, but keep the first analysis before `/speckit.implement` so gaps are caught while the plan and tasks can still be adjusted.
 
 ### Step 1: Install Specify
 
@@ -83,7 +83,7 @@ uvx --from git+https://github.com/github/spec-kit.git specify init <PROJECT_NAME
 /speckit.plan The application uses Vite with minimal number of libraries. Use vanilla HTML, CSS, and JavaScript as much as possible. Images are not uploaded anywhere and metadata is stored in a local SQLite database.
 ```
 
-Then generate a quality checklist with `/speckit.checklist` once the plan exists:
+Then generate quality checklists with `/speckit.checklist` once the plan exists:
 
 ```bash
 /speckit.checklist
@@ -160,7 +160,7 @@ Be specific about your tech stack and technical requirements:
 
 ### Step 5: Validate the Spec
 
-Validate the specification checklist using the `/speckit.checklist` command:
+Generate quality checklists to validate the specification using the `/speckit.checklist` command:
 
 ```bash
 /speckit.checklist