fix(mcp): follow tools/list pagination cursors

[Zheng-Lu]

Summary

Follow MCP tools/list pagination so discovery includes tools beyond the first page.

• Preserve list_tools(None) for the first request and pass each subsequent cursor through unchanged, including empty strings: cursors are opaque tokens.
• Finish only when nextCursor is absent. Return typed PaginationLoop for a repeated cursor and PaginationExceeded after 32 pages instead of returning a partial list.
• Apply the existing 60-second timeout to the complete traversal; propagate failures from any page.

The explicit loop preserves first-page wire compatibility and adds termination guards missing from rmcp 1.8.0's list_all_tools().

Test Plan

• Deterministic Python stdio MCP server exercises multi-page discovery, exact empty-cursor forwarding, repeated-cursor errors, and runaway pagination.
• The empty-cursor and repeated-cursor regressions failed before the review fix and pass afterward.
• All 9 MCP client tests passed after the final patch; core library: 688 passed, 3 PostgreSQL-gated tests ignored.
• cargo clippy -p agentic-server-core --all-targets -- -D warnings passed.
• pre-commit run --all-files passed.

[franciscojavierarceo]

patched empty-cursor forwarding and repeated-cursor errors, with regressions verified before and after the fix. all 688 core tests, Clippy, and pre-commit checks pass locally.