refactor: simplify MCP navigation targets

[jlitola]

Summary

• make MCP search, code_files, code_grep, and experimental code_diff accept compact string targets only
• preserve CLI syntax, normalized service requests, outputs, filters, and legacy read compatibility
• reduce stable serialized catalog size from 50,851 to 42,421 Unicode characters (8,430 / 16.6%) without a token-cost claim
• align current tool, skill, guardrail, CodeDiff, and repository-target documentation; retain exhaustive grammar in shared guidance
• record later product-gated simplification phases in the implementation plan

Compatibility

This intentionally removes structured MCP target objects. The change fragment gives package, repository, and site migration examples. CLI syntax is unchanged. read continues to advertise its code_read / docs_read replacement role, and Ask pointer projection remains covered.

Validation

• bun test — 4,752 passed, 0 failed
• focused implementation/parity/protocol suites — 122 + 210 passed
• descriptor/server suite — 111 passed
• bun run typecheck
• bun run lint — passed with existing warnings in unchanged repository-target code
• bun run build
• bun run validate:packages
• bun run plugins:generate / bun run plugins:check — 10 assets, no generated diff
• bun run smoke:mcp — stable and experimental live cohorts passed, including every changed compact target call
• source and built unauthenticated CLI smoke passed
• built stable and experimental MCP registration smoke passed
• Claude descriptor-only intent eval — 4/4 workloads succeeded, 18 MCP calls, no CLI fallback, no object targets, no reported failed calls, no validation violations
• Codex 0.154.0 Luna/high descriptor-only intent eval — 4/4 workloads succeeded with high confidence, 32 MCP calls, no CLI fallback, compact string targets in every affected tool call, no reported failed calls, no validation violations
• Luna pre-flight clean; internal code review clean after one documentation correction; external Opus review clean after two minor copy/test fixes

Evidence limitations

• One source CLI live smoke run received an incomplete Express repo-docs response on its 57th step. The exact follow-up returned 130 pages including 18 complete repo-backed pages, and the later live MCP smoke passed the same docs contract. Source CLI unauthenticated and built smoke gates passed.