fix(readme): correct OpenAPI version badge and SAT quick-start example

[dmchaledev]

Summary

• Badge/prose version mismatch: The README badge and overview text claimed "OpenAPI 3.1" for both specs, but sat/openapi.yaml declares openapi: 3.0.3. Updated the badge to 3.0/3.1 and the prose to list each spec's version explicitly.
• Broken SAT quick-start example: The "SAT — Enroll a User" section called POST /sat/v1/users with a body of {"email": ..., "group_id": ...}. In the spec, POST /users/ is the admin user-management endpoint (requires modify_system permission) — it creates system users, not campaign targets. Replaced it with a correct GET /api/campaigns/ call (returns the authenticated user's campaigns, no special permissions required) and updated the section title accordingly.

Changes

README.md only — no spec or CI changes.

Before	After
Badge: OpenAPI 3.1	Badge: OpenAPI 3.0/3.1
Prose: "OpenAPI 3.1 specifications"	Prose: "OpenAPI specifications (ASM: 3.1, SAT: 3.0)"
Table: OpenAPI 3.0 spec for the SAT REST API	Table: OpenAPI 3.0.3 spec for the SAT REST API
Example: POST /sat/v1/users with enrollment body	Example: GET /api/campaigns/

Test plan

• Confirm badge renders correctly in GitHub preview
• Confirm the SAT curl example matches a real endpoint in sat/openapi.yaml (GET /campaigns/ at line 625)

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