chore: add cache to imrpve integration test runs in the CI (build once, reuse across matrix)

[mojtaba-esk]

Describe your changes and provide context

This PR proposes to build the localnode image once in a dedicated job (base from GHCR or build+push, app with GHA cache, then push to ttl.sh with commit-SHA tag). All 14 matrix test jobs pull that image and run the cluster/tests instead of building. Makefile adds build-docker-node-app and drops proxy/local-only logic; Dockerfiles use ubuntu:25.04.

Testing performed to validate your change

[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	Feb 20, 2026, 11:52 AM

[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	Feb 19, 2026, 10:20 AM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.42%. Comparing base (933111a) to head (e184bd6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2932   +/-   ##
=======================================
  Coverage   68.42%   68.42%           
=======================================
  Files           5        5           
  Lines         456      456           
=======================================
  Hits          312      312           
  Misses        114      114           
  Partials       30       30           

Flag	Coverage Δ
sei-db	68.42% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

🚀 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.