fix: require a collection for every release (#286)

[Mehrn0ush]

Summary

• Every component/product release has a TEA Collection (may be empty `artifacts: []`)
• Empty first version uses `INITIAL_RELEASE`; first artifacts publish as version 2
• Make `artifacts` required on `collection`; `latestCollection` stays required
• `/collection/latest` `404` means the release is unknown
• Align collection docs: `createdDate`, `COMPONENT_RELEASE` / `PRODUCT_RELEASE`

Test plan

• Skim README, tea-requirements, tea-collection.md, OpenAPI `collection` + both `/collection/latest`

Thanks @taleodor

Closes #286

[taleodor]

Two edits and this is good. (1) The component-release-with-collection example is now inconsistent with the rule: version: 2 with INITIAL_RELEASE and artifacts. Make it version: 1, or keep 2 and use ARTIFACT_ADDED. (2) In tea-collection.md, replace the quoted "version 1 is whatever was first observable" line with plain prose, e.g. "In both cases version 1 is the first collection a client could have retrieved." While in that list, the empty bullet above artifacts can go.

Also, Line 333 is a stray empty bullet ( -) between updateReason and artifacts. Pre-existing, but the list is being edited in this PR, so pls correct.

[Mehrn0ush]

Thanks.
Fixed both: example now uses ARTIFACT_ADDED at version 2 with artifacts; tea-collection.md uses the plain "first collection a client could have retrieved" wording and drops the empty bullet.