fix(cli): apply --files startup seed in virtual shell

[savageops]

Summary

The interactive shell accepted --files and parsed JSON input, but never applied those files to the runtime filesystem.

This PR wires --files into shell startup by seeding the OverlayFS before constructing Bash.

Why

This is a user-facing contract bug: a documented option was a silent no-op.

Changes

• Add seedOverlayFiles helper for startup fixtures.
• Call helper in src/cli/shell.ts constructor path.
• Add focused tests for seeded startup files and omitted-file behavior.

Validation

• pnpm test:run src/cli/shell-files.test.ts (2/2 passing)

Risk

Low.

• Change is isolated to shell startup path.
• No command/runtime parser/interpreter behavior changed.
• Covered by targeted tests.

[vercel]

@savageops is attempting to deploy a commit to the Vercel Labs Team on Vercel.

A member of the Team first needs to authorize it.