feat: comprehensive logging overhaul for better debugging and diagnostics

[Copilot]

Summary

Overhauls logging across the extension to make debugging environment discovery and startup issues much easier for users and maintainers. The goal is that when something goes wrong (environments not found, startup stuck, selection not persisting), the Output panel logs tell a clear story of what happened and where.

Changes (10 files, +47/-25 lines)

1. Extension initialization progress (extension.ts)

Added traceInfo at each stage boundary with timing so users can see exactly where startup gets stuck:

• Native finder initialization start/complete with duration
• Manager registration start/complete
• Environment selection start/complete
• Final "Extension setup complete" with total time

2. Discovery START/END logging (internal.api.ts)

Every discovery operation now unconditionally logs:

• [Manager] Discovering environments... at start
• [Manager] Discovery complete: N environments found (X.Xs) at end
• (Previously only logged when slow >15s or on failure)

3. Fixed wrong log levels

• uvPythonInstaller.ts: traceError → traceWarn for curl/wget fallback (not an error)
• nativePythonFinder.ts: traceError → traceWarn for global-level workspace setting (config issue, not runtime error)
• envCommands.ts: traceInfo → traceVerbose for clipboard copy operations (too minor for info)

4. Error context disambiguation (terminalEnvVarInjector.ts)

4 previously identical "Failed to update environment variables" error messages now have distinguishing context: (global reload), (no workspace folder for URI), for workspace: <name>, (settings change)

5. Environment creation logging (envCommands.ts)

createEnvironmentCommand and createAnyEnvironmentCommand now log on success with the environment name.

6. Environment selection logging (envManagers.ts)

setEnvironment promoted from traceVerbose to traceInfo and logs unconditionally (not just when persisting settings), showing env name, ID, scope, and manager.

7. Pyenv discovery parity (pyenvUtils.ts)

Added discovery source logging to match other managers (conda, pipenv, poetry): PYENV_ROOT, home directory, pyenv-win, PATH lookup, and "not found" message. Also logs discovery count.

8. Discovery summary enhancement (telemetry/helpers.ts)

logDiscoverySummary now includes ALL managers in the summary (even those with 0 environments or errors), making it clear which managers were checked.

Validation

• ✅ Lint clean
• ✅ Type check clean
• ✅ 983 unit tests passing
• ✅ Code review passed
• ✅ CodeQL security scan passed