Align CI/CD and release automation with pgxschema

[kiro-agent]

This pull request was generated by @kiro-agent 👻

Comment with /kiro fix to address specific feedback or /kiro all to address everything.
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Brings the schema package's CI and release workflows in line with the patterns established in pgxschema.

Changes

CI Workflow (.github/workflows/ci.yml)

• Bump actions/checkout v4 → v6 and actions/setup-go v5 → v6
• Add a dedicated Vet job (go vet ./...) matching pgxschema's CI structure
• Update golangci-lint-action to use v2.11.4 with --timeout 2m
• Update codecov-action v4 → v5, move token to env block
• Rename coverage output from coverage.out to coverage.txt
• Remove redundant permissions, concurrency, and timeout-minutes blocks for cleaner config

Release Workflow (.github/workflows/release.yml)

• Switch from Python-based README scraping to awk-based CHANGELOG.md extraction (matching pgxschema)
• Use stricter semver tag pattern: v[0-9]+.[0-9]+.[0-9]+*
• Add module verification step (go build + go vet) after release creation
• Bump to actions/checkout@v6 and actions/setup-go@v6
• Remove concurrency and fetch-depth overrides

Config & Documentation

• .golangci.yml: Remove outdated run.go: '1.24' / timeout block (golangci-lint v2 handles this via CLI args)
• CHANGELOG.md: New file — full version history converted from README's "Version History" section into Keep a Changelog format

Not Changed

• go.mod — already at go 1.25.5, no update needed
• Linter selection in .golangci.yml — kept schema-specific linters (different from pgxschema due to multi-dialect SQL driver coverage)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.79%. Comparing base (9560662) to head (3163442).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #51   +/-   ##
=======================================
  Coverage   99.79%   99.79%           
=======================================
  Files          10       10           
  Lines         483      483           
=======================================
  Hits          482      482           
  Misses          1        1           

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