Add git tag support

[coinselor]

The script currently only supports building from git branches. This feature aims to support git tag refs enabling users to deploy specific release versions in addition to development branches.

Problem

The deployment script (lib/build.sh) only fetches and allows selection of git branches via get_branches(). Users cannot deploy specific tagged releases.

Proposed Solution

• Modify get_branches() to something like get_git_refs(): update to fetch both branches and tags using git ls-remote --refs
• Update clone_and_build() to handle both refs
• Clone logic: use git clone --branch <ref> <repository-url> (works for both branches and tags)
• Add missing non-interactive ref existence validation.
• Add tui support to show tags and branches in separate sections
• Variable names: rename ZNNSH_BRANCH_NAME to ZNNSH_GIT_REF for clarity
• CLI arguments: update cli to accept --tag arguments.

Files to modify:

• lib/build.sh
• lib/config.sh
• zenon.sh
• README.md

Acceptance Criteria

• Users can select from both branches and tags in interactive mode
• Non-interactive CLI accepts both branch names and tag names
• Visual distinction between branches and tags in selection UI
• Semantic version sorting for tags (v1.0.0, v1.1.0, v2.0.0, etc.)
• Backward compatibility maintained for existing branch-only deployments
• Proper error handling for invalid references
• Updated README reflecting new functionality