fix(shell): restore reliable interactive startup

[NathanFlurry]

• Restore reliable interactive and TTY defaults for just shell.
• Rebuild missing local dependencies, registry packages, sidecar binaries, and actor prerequisites on demand.
• Route managed WASM terminal calls through the authoritative sidecar PTY and cover the behavior.
• Document local shell setup and the thin-client/runtime ownership constraint.

[railway-app]

🚅 Deployed to the agentos-pr-1744 environment in agentos

Service	Status	Web	Updated (UTC)
agentos	😴 Sleeping (View Logs)	Web	Jul 13, 2026 at 4:36 am

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🚅 Environment agentos-pr-1744 in rivet-frontend has no services deployed.