Prepare Base v1.2.0 release

[codeforester]

Summary:

• Move post-1.1.0 release notes into a dated Base 1.2.0 changelog section.
• Bump VERSION and README release examples to 1.2.0.
• Refresh current-release AI context and README status text for the workspace init release.

Validation:

• 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-120 bin/basectl release notes --version 1.2.0
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash BASE_CACHE_DIR=/private/tmp/base-release-120 bin/basectl release check --version 1.2.0

Fixes #1049