feat: verify Python parity for the current MCP read/write tool surface

[maehwasoo]

What

• add a Python parity boundary doc for the current MCP read/write tool surface, including current Node-only gaps and the migration gate
• add MCP docs coverage tests that keep the parity matrix aligned with the live read/write tool surface
• add Python parity contract tests for scoped retrieval, missing-context behavior, explicit write refusal, and failure-code documentation sync

Why

• issue feat: verify Python parity for the current MCP read/write tool surface #182 needs an explicit parity target before any later runtime removal can be evaluated safely

• document the current Python baseline gaps instead of implying that MCP read/write parity already exists

• keep parity-critical contracts under automated verification so the migration boundary does not drift

• Fixes feat: verify Python parity for the current MCP read/write tool surface #182

How

• add docs/architecture/python-mcp-parity.md and link it from the docs indexes
• extend packages/mcp/test/docs.mcpToolingConsistency.test.ts to verify that the parity matrix covers the live MCP tool surface
• add apps/api/tests/test_parity_contract.py and seed combined tag coverage for scoped retrieval checks
• validate with pnpm check:ci