docs: add Spring Break 2x usage promo note + ICM evaluation

- Guide: documented Anthropic March 13-27 2026 promotion (2x limits
  outside 5-11am PT / all weekends), with CET timezone conversion for
  European users
- Resource evaluation: ICM Infinite Context Memory MCP server (score 3/5)
- CHANGELOG: both entries under [Unreleased]

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/resource-evaluations/icm-infinite-context-memory.md

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+# Resource Evaluation: ICM (Infinite Context Memory)
+
+**Date**: 2026-03-14
+**URL**: https://github.com/rtk-ai/icm
+**Type**: GitHub repository / MCP server
+**Score**: 3/5 — Integrated
+**Decision**: Added as section after Kairn in `guide/ultimate-guide.md` (~line 11365)
+
+---
+
+## Summary
+
+ICM is a persistent memory MCP server from the rtk-ai team (same authors as RTK/Rust Token Killer). It provides a dual memory architecture: "Memories" (episodic, configurable decay) and "Memoirs" (permanent knowledge graph with 9 typed relation types). Distributed as a single Rust binary with zero external dependencies, installable via Homebrew.
+
+### Key Points
+
+- Single Rust binary, SQLite, zero deps — Homebrew install
+- Dual architecture: episodic decay + permanent knowledge graph in one tool
+- Hybrid search: BM25 30% + vector similarity 70%
+- Auto-deduplication (>85% similarity blocked)
+- Auto-extraction: pattern hooks, pre-compaction, session-start
+- Supports 14 editors/clients (Claude Code, Cursor, VS Code, Windsurf, Zed, Amp, Cline, etc.)
+- 52 stars, 55 commits as of March 2026
+- License: Source-Available (free for individuals and teams ≤20; enterprise license required above)
+
+---
+
+## Scoring
+
+| Criterion | Score |
+|-----------|-------|
+| Relevance to Claude Code users | 4/5 |
+| Differentiation from existing content | 3/5 |
+| Maturity / adoption signal | 2/5 |
+| License openness | 2/5 |
+| **Overall** | **3/5** |
+
+---
+
+## Comparison vs Existing Guide Content
+
+| Feature | doobidoo | Kairn | ICM |
+|---------|----------|-------|-----|
+| Language | Python | Python | Rust (single binary) |
+| Install | pip | pip | Homebrew |
+| Episodic decay | No | Yes (biological) | Yes (configurable) |
+| Permanent knowledge graph | No | Yes | Yes (Memoirs) |
+| Auto-extraction | No | No | Yes |
+| License | MIT | MIT | Source-Available |
+
+Main differentiator: zero-dependency Rust binary lowers install friction for users who struggle with Python environments. Conceptual overlap with Kairn (knowledge graph + decay) is real but the runtime difference is meaningful.
+
+---
+
+## Benchmarks
+
+All benchmarks below are **vendor-reported by rtk-ai** — not independently verified.
+
+**Storage performance (1000 ops, 384d embeddings)**:
+- Store (no embeddings): 34.2 µs/op
+- Store (with embeddings): 51.6 µs/op
+- FTS5 full-text search: 46.6 µs/op
+- Vector search (KNN): 590.0 µs/op
+- Hybrid search: 951.1 µs/op
+
+**Agent efficiency (Haiku model, multi-session)**:
+- Session 2: 29% fewer turns, 32% less input context, 17% cost reduction
+- Session 3: 40% fewer turns, 44% less context, 22% cost reduction
+
+**Knowledge retention (10 questions)**:
+- Without ICM: 5%
+- With ICM: 68%
+
+Note: The knowledge retention benchmark uses a sample of 10 questions on Haiku — too narrow for generalization.
+
+---
+
+## Fact-Check
+
+| Claim | Status | Source |
+|-------|--------|--------|
+| Storage: 34.2 µs/op | ✅ | README benchmarks section |
+| Hybrid search: ~951 µs/op | ✅ | README benchmarks section |
+| 29-40% turn reduction | ✅ present / ⚠️ vendor-reported | README — rtk-ai self-evaluation |
+| 68% vs 5% knowledge retention | ✅ present / ⚠️ vendor-reported, n=10 | README |
+| Source-Available license, free ≤20 | ✅ | LICENSE file |
+| 9 Memoir relation types | ✅ | README full list |
+| 14 supported clients | ✅ | `icm init` documentation |
+| 52 stars | ✅ | GitHub as of 2026-03-14 |
+
+No hallucinations detected. All figures present in the source README.
+
+---
+
+## License Note
+
+Source-Available license. Free for individuals and teams of up to 20 people. **Enterprise license required for organizations above 20 people.** Contact: license@rtk.ai
+
+This was flagged in the guide entry with an explicit callout. Teams should verify their org size before deploying.
+
+---
+
+## Integration Location
+
+- New section: `guide/ultimate-guide.md` after Kairn (~line 11365), before "MCP Memory Stack: Complementarity Patterns"
+- Comparison matrix updated: ICM column added with Runtime and License rows
+
+## Upgrade Trigger
+
+Revisit for 4/5 if:
+- Benchmarks independently verified by community
+- Adoption exceeds 500+ stars with sustained commit activity
+- License changes to MIT/Apache