security: clamp list_pages and get_ingest_log limits

[garagon]

Summary

Several gbrain MCP operations accept a limit parameter that controls how many
results to return. The search and query operations were already capped at 100 via
clampSearchLimit (fixed in v0.9.1). Two other operations were not:

• list_pages: (p.limit as number) || 50 — no cap
• get_ingest_log: (p.limit as number) || 20 — no cap

The problem: an MCP caller can pass {limit: 10000000} and force the engine to
return an unbounded result set, consuming memory on the server.

What the fix does

Both operations now use clampSearchLimit(p.limit, defaultValue) — the same function
that already caps search and query. The ceiling is MAX_SEARCH_LIMIT = 100.
Normal usage (limit under 100) is unaffected.

Changes

src/core/operations.ts

• Import clampSearchLimit from engine.ts
• list_pages handler: clampSearchLimit(p.limit, 50)
• get_ingest_log handler: clampSearchLimit(p.limit, 20)

Validation

• bun test test/parity.test.ts — 10 pass (operation contract intact)
• bun test test/search-limit.test.ts — 11 pass (clamp logic verified)
• Runtime: clampSearchLimit(10000000, 50) → 100, clampSearchLimit(undefined, 50) → 50