feat: add Wasmtime executor and modular VM packages

[NathanFlurry]

• Add production Wasmtime and isolated Wasmtime-threads executors while retaining V8 for JavaScript and V8-WASM compatibility.
• Move reusable POSIX behavior into the shared VM/kernel layers, split concrete executors into feature-gated crates, and preserve bounded lifecycle, resources, cancellation, and typed errors.
• Flatten the TypeScript runtime packages, consolidate the native sidecar, and archive browser reference code outside active builds.
• Support embedding agentos-vm directly with no sidecar, client, or executor; gate persistence, package tooling, crypto/TLS, OXC, WASM, Tokio, and protocol dependencies out of the minimal build.
• Add dependency and size regressions for the 754 KiB embedded VM binary, plus isolated executor/storage feature matrices.
• Matrix the maintained WASM, software, filesystem, networking, PTY, safety, release, benchmark, and soak coverage across V8 and Wasmtime.

[railway-app]

🚅 Deployed to the agentos-pr-1846 environment in agentos

Service	Status	Web	Updated (UTC)
agentos	😴 Sleeping (View Logs)	Web	Jul 30, 2026 at 11:06 pm

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🚅 Environment agentos-pr-1846 in rivet-frontend has no services deployed.