WASM shell does not execute shebang scripts from VFS

The WASM sh (from coreutils) only resolves commands registered in its internal WASM binary command table. It cannot execute #!/bin/sh scripts stored in the virtual filesystem, even when they are in a PATH directory and have execute permissions.

This breaks the agentOS host tool shim workflow. Tool shims are shell scripts generated at /usr/local/bin/agentos-{name} that call the tools RPC server via http-test. Running exec("agentos-weather get --city London") returns "command not found" because the shell never checks the VFS for executable files.

Expected behavior (POSIX)

When resolving a command, sh should:

1. Search each directory in PATH for a file matching the command name
2. If found and executable, read the first line for a shebang (#!)
3. Execute the file with the interpreter specified in the shebang

Where to fix

secure-exec WASM shell command resolution. The shell needs to fall back to VFS file lookup after the WASM command table miss.

Secondary issue

The http-test WASM binary (used by the shims to make HTTP requests) is defined in agent-os-registry/native/crates/commands/http-test/ but is not included in any installable software package. It needs to be bundled in @rivet-dev/agent-os-common or replaced with curl.