Backport release/v6.6: Update v6.6 change log in prep to cut v6.6.4 patch

[seidroid]

Backport of #4466 to release/v6.6.

[cursor]

PR Summary

Low Risk
Documentation-only changelog edit with no code, config, or state-machine impact.

Overview
Updates the v6.6 section of CHANGELOG.md ahead of cutting a v6.6.4 patch on release/v6.6 (backport of #4466).

It prepends three new sei-chain bullets at the top of the list: #4448 (initialize the app from the last header on frozen restart), #4056 (bump to v6.6.3 for a prior patch), and #4055 (prior v6.6.3 changelog backport). No runtime or config changes—release notes only.

^{Reviewed by Cursor Bugbot for commit a21aa38. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Oct 6, 2026, 10:17 AM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.17%. Comparing base (1f9afeb) to head (a21aa38).
⚠️ Report is 1 commits behind head on release/v6.6.

Additional details and impacted files

@@               Coverage Diff                @@
##           release/v6.6    #4468      +/-   ##
================================================
- Coverage         59.07%   58.17%   -0.91%     
================================================
  Files              2231     2157      -74     
  Lines            184613   175895    -8718     
================================================
- Hits             109057   102320    -6737     
+ Misses            65723    64447    -1276     
+ Partials           9833     9128     -705     

Flag	Coverage Δ
sei-db	69.80% <ø> (ø)
sei-db-state-db	?

Flags with carried forward coverage won't be shown. Click here to find out more.
see 74 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.