docs: add CHANGELOG covering v1.0.0 and v1.1.0 (cert chain support)

[krakenhavoc]

Weekly Documentation Audit — 2026-05-19

Documentation gaps found in PRs merged 2026-05-12 to 2026-05-19

New docs added

CHANGELOG.md — this file did not previously exist in the repo.

The cert chain / fullchain output feature shipped this week (dependent on KrakenKey/app v0.4.0 and KrakenKey/cli v0.2.0) but there was no CHANGELOG to record the release history.

Covers:

Version	Date	Highlights
v1.0.0	2026-04-13	Initial release — krakenkey/cert-action@v1
v1.1.0	2026-05-18	chain-out and fullchain-out inputs; chain_pem and fullchain_pem outputs

Suggested version bump

Tag v1.1.0 if not already created. The CHANGELOG documents this as the version that adds intermediate chain and full chain PEM outputs.

Test plan

• Confirm v1.1.0 git tag exists (or create it)
• Verify CHANGELOG dates match actual merge/release dates
• Confirm chain-out / fullchain-out input names match action.yml

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