Release Base v1.4.0

[codeforester]

Prepare and publish Base v1.4.0.

Scope:

• update release metadata (VERSION, CHANGELOG.md, README, .ai-context)
• validate release readiness from a clean worktree
• merge the release-prep PR
• publish the v1.4.0 GitHub release
• update the Homebrew tap after the tag is available

This release closes the current macOS-focused 1.4 train before the Ubuntu runtime-support work moves into v1.5.0.

[codeforester]

Base v1.4.0 release is complete.

Completed:

• Release-prep PR: Prepare Base v1.4.0 release #1325
• Published release: https://github.com/basefoundry/base/releases/tag/v1.4.0
• Published tag: https://github.com/basefoundry/base/tree/v1.4.0
• Homebrew tap issue: Update Base formula to v1.4.0 homebrew-base#61
• Homebrew tap PR: Update Base formula to v1.4.0 homebrew-base#62

Validation evidence:

• git diff --check
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash env -u BASE_HOME ./bin/base-test
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash BASE_CACHE_DIR=/private/tmp/base-release-140 ./bin/basectl release check --version 1.4.0
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash BASE_CACHE_DIR=/private/tmp/base-release-140 ./bin/basectl release publish --version 1.4.0 --dry-run
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash BASE_CACHE_DIR=/private/tmp/base-release-140 ./bin/basectl release publish --version 1.4.0 --yes
• Tap formula ruby -c Formula/base.rb
• Tap formula git diff --check
• Tap archive checksum verified as 0eafa8e52cf7be9a9b3ff4f2c663b3b3b44926c38bb0dafb1bf8d60de99fa8b0

Note: local brew audit --new --formula Formula/base.rb did not reach formula audit because this host failed while building Homebrew's vendored json gem for RuboCop under portable Ruby 4.0.5_1.