feat: add MCP server with stdio transport and project knowledge base

[superops-team]

Overview

Add Model Context Protocol (MCP) server support to OKF, enabling AI agents to load, query, search, and lint knowledge bundles through standard MCP tools over stdio transport.

Changes

MCP Server Implementation (pkg/mcp/)

• protocol.go — Full JSON-RPC 2.0 message types and MCP protocol types (Initialize, Tools, Resources, Prompts)
• tools.go — Tool registry with 7 core tools:
  • okf_load_bundle — Load knowledge bundle from directory
  • okf_bundle_stats — Get bundle statistics (types, status, trust tiers, stale count)
  • okf_list_concepts — List concepts with optional type filter
  • okf_get_concept — Get full concept details serialized as Markdown
  • okf_search — Full-text search with type/tag filters
  • okf_lint_bundle — Lint entire bundle with optional strict mode
  • okf_lint_concept — Lint single concept
• server.go — stdio transport main loop with full message dispatching
• convert.go — Type conversion helpers between okf and parser packages

CLI Integration

• Added okf mcp --bundle <path> subcommand to start the MCP server

Project Knowledge Base (docs/knowledge/)

6 OKF v0.2 format documents documenting the project:

• index.md — Knowledge base index
• core-types.md — Core type system (v0.2)
• parser.md — Markdown + YAML parser
• lint.md — Lint rules and error codes
• mcp-server.md — MCP server architecture and usage
• cli.md — CLI command reference

Design Specification (openspec/changes/okf-mcp-server/)

• proposal.md — Change proposal
• design.md — Technical design
• specs/okf-mcp-server/spec.md — MCP server specification

Testing

• test_mcp.py — End-to-end test script with 11 test cases
• All tests pass: initialize, tools/list, 7 tool calls, resources/list, prompts/list, ping

MCP Client Configuration

{
  "mcpServers": {
    "okf": {
      "command": "okf",
      "args": ["mcp", "--bundle", "/path/to/knowledge"]
    }
  }
}

Dependencies

This PR depends on the v0.2 spec upgrade (OKF v0.2 types: TrustTier, ConceptStatus, Sources, Verified, Attested Computation, etc.).

Verification

• go build ./... passes
• go test ./... passes
• End-to-end MCP test: 11/11 tests pass
• Knowledge base lint passes (0 errors)