[Changelogs] Fix derived lifecycle for date-based bundles ("ga" instead of "preview")

[lcawl]

Describe the bug

Problem

For standard (non-github_release) changelog bundle profiles, {lifecycle} in output_products / products / output is derived from the version argument via VersionLifecycleInference.InferLifecycle.

That works for semver (9.2.0 → ga, 9.2.0-beta.1 → beta). For ISO date targets used by serverless releases, it is wrong:

Argument	Actual {lifecycle}	Expected
2026-07-21	preview	ga

Cause: InferLifecycle treats the first - as a semver prerelease delimiter. For 2026-07-21 it takes 07 as an unknown prerelease tag and falls through to preview.

Example profile that surfaces this:

serverless-release:
  output_products: "cloud-serverless {version} {lifecycle}"
  output: "cloud-serverless/kibana-{version}.yaml"

docs-builder changelog bundle serverless-release 2026-07-21 ./docs/temp/serverless-prs.txt

writes:

products:
- product: cloud-serverless
  target: 2026-07-21
  lifecycle: preview   # incorrect

This matches the documented contract (profile mode does not take a separate lifecycle CLI arg; {lifecycle} means “derive”). The bug is the derived value for dates, not that derivation exists.

Expected behavior

The default lifecycle for date-based releases should be "ga" same as for versioned releases like "9.2.0".
If non-GA releases are desired, that would need a separate profile with an explicit lifecycle, as is currently documented.

Steps to reproduce

The preview value exists in all recent Kibana Serverless release bundles, for example: elastic/kibana#280230

Tooling

• docs-builder
• migration tooling
• I'm not sure

[lcawl]

A quick AI proposal to fix this:

Proposed solution

Code

In VersionLifecycleInference.InferLifecycle (src/Elastic.Documentation.Configuration/Changelog/VersionLifecycleInference.cs):

1. Detect ISO dates (YYYY-MM-DD) and return ga.
2. Leave existing semver prerelease rules unchanged.

Add unit tests, including 2026-07-21 → ga, plus the existing semver cases.

Optional follow-up in consuming repos: regenerate bundles that already wrote lifecycle: preview for date-based releases. Profiles may keep {lifecycle}, hardcode ga / preview / beta, or omit lifecycle entirely — same options as semver. Non-ga date releases should hardcode lifecycle (expected to be rare).

Docs

In lifecycle-inference docs (e.g. docs/cli/changelog/cmd-bundle.md, and related contribute/example config as needed):

1. Add a date row to the standard-profile table: 2026-07-21 → {lifecycle} = ga.
2. Clarify the three YAML patterns for both semver and date-based profiles:
   • omit lifecycle → field absent
   • {lifecycle} → derived
   • hardcoded (ga / beta / preview) → explicit
3. Note that non-ga date-based releases are exceptional and should hardcode the lifecycle.