v0.5.0 — moshcode upgrade 🤘

🎸 moshcode v0.5.0 — one command to update everything

New moshcode upgrade (alias update; TUI: /upgrade). With no args it updates everything that has a newer version — moshcode itself + every installed engine:

moshcode upgrade            # moshcode + all installed engines
moshcode upgrade claude     # just one engine (any name/alias)
moshcode upgrade self       # just moshcode itself
moshcode upgrade engines    # all installed engines, skip self

Conductor pattern — no vendoring. Each engine is updated with its own native updater when it has one (opencode upgrade, aider --upgrade) and re-run through its idempotent installer otherwise (claude/codex/gemini → npm i -g, which fetches latest). moshcode self-updates via its install.sh update path.

• Streams each tool's own progress; prints a per-tool ✓/✗ and a final summary.
• Interactive runs hand back to the mosh pit; piped/CI exit non-zero if any upgrade failed.
• There's no plugin system yet, so "everything" = moshcode + engines today.