Add MCP server tool call adapter

[op-simoneromeo]

Refreshes the same MCP server tool-call adapter slice from #216 against current master, so the accepted UGig work remains reviewable after the original fork branch became conflict-blocked.

Changes:

• adds a core MCP stdio JSON-RPC tool-call helper
• exposes the MCP helper through @profullstack/sh1pt-core
• adds the mcp-servers CLI adapter category
• adds a public Penpot MCP server adapter package following the existing adapter-package pattern
• adds focused Penpot MCP adapter tests

Validation:

• pnpm --filter @profullstack/sh1pt-core typecheck
• pnpm --filter @profullstack/sh1pt-mcp-server-penpot typecheck
• pnpm --filter @profullstack/sh1pt-mcp-server-penpot build
• pnpm vitest run packages/mcp-servers/penpot/src/index.test.ts
• git diff --check origin/master...HEAD

Validation limit:

• pnpm --filter @profullstack/sh1pt typecheck currently fails on current master in packages/cli/src/commands/scale.ts because readFileSync and existsSync are imported twice there; this PR does not touch that file.

Refs #214 and #216.