Split MCP server core tool router

[yvette-carlisle]

Summary

• Split the MCP server core #[rmcp::tool_router] implementation into app/server/tools/core.rs.
• Kept parent server.rs focused on module ownership, runtime support imports, and tool router composition.
• Updated source-contract tests to read the full MCP server module tree instead of only server.rs.

Validation

• cargo make fmt-rust
• cargo make check-rust
• cargo nextest run -p elf-mcp registers_all_tools recall_debug_panel_rejects_context_override_params searches_notes_tool_description_mentions_payload_level_shapes --all-features (3 passed, 16 skipped)
• cargo nextest run -p elf-eval --test real_world_job_benchmark dreaming_review_queue_report_wires_reviewable_policy_contract graph_topic_map_report_wires_source_backed_graph_lite_readback --all-features (2 passed, 91 skipped)
• cargo make fmt-rust-check
• git diff --check
• cargo make lint-vstyle
• cargo make lint-rust
• cargo make test-rust (379 passed, 92 skipped)
• cargo make check (379 passed, 92 skipped)
• Docker-backed cargo make test-rust-integration (92 passed, 379 skipped)
• Docker-backed cargo make check-trace-gate

Review

• Scout selected the MCP core tool registration boundary as a strong modularization slice.
• Skeptic passed with no findings after checking the staged diff, normal module boundary, moved router body equivalence, visibility, test adaptation, and validation evidence.