fix: add default input schemas for MCPB tools

[jstar0]

Summary

This updates MCPB bundle deploy payload generation so tools declared in an MCPB
manifest are converted into registry-compatible tool entries.

Fixes #787.

Changes

MCPB manifests can declare tools with name and optional description, but
they cannot include the registry inputSchema field. The deploy payload now
preserves each tool name and string description, then adds a default empty
object schema, {"type":"object"}.

This lets valid .mcpb bundles with declared tools publish without sending
tools that are missing the required schema field.

Before this change, publishing a .mcpb bundle forwarded
manifest.tools directly into serverCard.tools. That made bundles valid for
MCPB packaging fail registry validation during publish, because MCPB tool
entries do not carry inputSchema.

Verification

pnpm run check
pnpm test
pnpm run typecheck
pnpm run build