simulate: Node agent support, --view mode, and TUI/start UX fixes

[u9g]

Ports our simulate work onto the Node-support branch (brian/agent-session-node-support). These changes originated on an older fork of the simulate TUI, so they're re-applied as fresh edits rather than cherry-picks.

Agent start / Node support

• Use normalizeLogLevel for the agent's --log-level.
• Only pass --log-format colored for Python (the Node CLI rejects it).
• Default Node entrypoints main.ts / src/main.js (and src/ fallbacks).
• Refuse entrypoint auto-discovery when package.json defines a build task and no entrypoint was given (build output paths are nontrivial).
• Drop the Python-only guard so Node agents can be simulated.

lk agent simulate --view <runID>

• New --view flag / modeView to open a pre-existing simulation.
• Print the reopen command (lk agent simulate --view <runID>) when the TUI closes.

TUI UX

• → / enter to open a simulation's detail; ← / esc / backspace to go back (hints updated).
• Richer agent-exit errors: include the command used to start the agent and its recent output (or "exited with no output").
• Quit the TUI when the agent fails to register instead of hanging.

Intentionally not ported (already present in a different form on this branch): the exit()/confirmQuit refactor and the s save-scenario key — this branch has its own save overlay and quit handling.

Builds clean with go build and go vet -tags console.