feat: add knowledge.enabled option to disable LTM system

[BYK]

Summary

Adds a knowledge.enabled config option (default: true) in .lore.json that disables the entire long-term knowledge subsystem while keeping conversation recall and context management fully active.

This addresses feedback from users who prefer manual context management but still want the conversation search capabilities.

When knowledge.enabled: false:

• ❌ Curator (knowledge extraction) — skipped
• ❌ Knowledge injection into system prompt — skipped
• ❌ AGENTS.md import/export — skipped
• ❌ Oversized entry pruning — skipped
• ✅ Temporal storage — active
• ✅ Distillation — active
• ✅ Gradient context manager — active
• ✅ Recall tool (temporal + distillation search) — active
• ✅ Overflow auto-recovery — active

Config example

{ "knowledge": { "enabled": false } }

Changes

• src/config.ts — Added knowledge section with enabled boolean
• src/index.ts — Guarded 6 knowledge code paths with cfg.knowledge.enabled
• src/reflect.ts — Added knowledgeEnabled parameter, skips ltm.search() when false
• test/config.test.ts — 4 new tests for schema + load behavior
• README.md — New Configuration section documenting all .lore.json options