docs: complete DHIS2 immunization tutorial

[jeremi]

Summary

• download the full DHIS2 OpenAPI document from /api/openapi.yaml, which declares the tracked-entity operation and response schema used by the tutorial
• document the nonfatal schema warnings emitted by evidencectl source suggest
• complete the Evidence Gateway terminology update, remove the draft gate marker, and mark the replayed tutorial current
• add complete local cleanup commands

User impact

Readers can now complete the source-authoring and request-preparation journey instead of failing first on a missing OpenAPI operation and then on bounded-integer verification.

Dependency

• Depends on fix(evidence): verify bounded integer local responses #652, which fixes the bounded-integer local verification failure found by the full tutorial replay.

Verification

• authenticated to the public DHIS2 2.43.1 demo with its published shared credentials
• downloaded the full public OpenAPI document and ran the tutorial's exact evidencectl source suggest selections successfully
• replayed every authored YAML and Rhai fence in a clean project
• started local Evidence and Mint services and completed evidencectl request prepare with sanitized local inputs
• did not send a live subject request or retain a demo record identifier
• npm run check:markdown -- src/content/docs/tutorials/issue-immunization-evidence-from-dhis2.mdx
• node scripts/run-vale.mjs src/content/docs/tutorials/issue-immunization-evidence-from-dhis2.mdx
• npx astro check (0 errors; one existing deprecation hint)