Publish v2 API and module manifest

[codeforester]

Closes #225

What changed

• Added base_api_manifest.yaml, a versioned v2.0.0 API/module manifest covering the namespace contract, modules, dependencies, Bash minimum, symbols, API metadata, environment/globals, optional commands, documentation, tests, and artifact membership.
• Added the Bash-native scripts/api-manifest checker/generator. It validates missing and duplicate symbols, source drift, unsafe paths, dependency cycles, packaging membership, metadata, and stale generated documentation, and exposes manifest-driven source/test/artifact paths.
• Added generated docs/api-reference.md and the schema/consumer guide at docs/api-manifest-schema.md.
• Rewired tests/validate.sh to discover module source files, BATS suites, ShellCheck targets, and artifacts from the API manifest rather than a second hardcoded module inventory.
• Corrected STANDARDS.md and the changelog to use the finalized base_ public namespace.
• Updated Publish a machine-readable API and module manifest #225 to use the v2.0.0 RC baseline and explicitly preserve the single-file library boundary.

Design notes

base_manifest.yaml remains the Base release/developer-tooling manifest. The API
manifest is separate so Base's existing manifest schema is not extended with
library-specific fields. The API manifest uses a documented line-oriented YAML
subset and has no mandatory Python, Ruby, yq, or jq runtime for consumers.

Validation

• ./tests/validate.sh </dev/null
• 486 BATS tests passed
• ShellCheck error profile passed
• Bash logging/release smoke tests passed
• All eight caller-option combinations passed
• tests/lint-warnings.sh reports only the repository's existing warning baseline
• git diff --check passed