fix(shell): restore reliable interactive startup

[NathanFlurry]

• Restore interactive and TTY defaults while keeping just shell a transparent argument-forwarding shim.
• Repair missing workspace links, software payloads, runtime entrypoints, and local native binaries before startup.
• Prepare the filtered RivetKit workspace and actor plugin automatically for just shell --actor.
• Route managed WASM terminal RPCs through the sidecar PTY instead of standalone fallbacks.
• Prevent duplicate default software and stale binary overrides from breaking local shell creation.
• Document and test the direct and actor shell workflows with CLI, actor-plugin, Brush PTY, Rust, and tmux coverage.

[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 1:46 am

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