Add comprehensive logging to plugin and app discovery so failed
target lookups are diagnosable. List available targets when a
requested name is not found. Replace bare except: with
except Exception and log the error.

Add comprehensive logging to the release-go discovery and build registry process

This PR adds detailed logging throughout the discovery and build pipeline in the release-go.py script, improving observability and debuggability of the build target discovery process. Key changes include:

• Standalone app discovery: Logs when the apps/ directory is missing, when scanning begins, when apps are found or skipped (with reasons), and a summary of discovered apps.
• Plugin discovery: Logs when the libs/ directory is missing, when scanning begins, when plugins are skipped (missing vite config, missing build script, skip keyword match, non-directory), when plugins are discovered, and a summary of discovered plugins.
• Build registry: Logs a summary after building, including total target count and breakdowns by type (app-shell, standalone, plugin), plus a debug-level list of all target names.
• Target filtering: Logs available targets when "all" is selected or when a requested target is not found, and improves the not-found warning message formatting.

Additionally, bare except clauses are replaced with except Exception as e: and now log the actual error, improving error visibility during discovery failures.