docs: Add multi-session/LLM continuity references

- Update README.md to prioritize PROJECT_STATE.md for new agents
- Add handoff instructions to implementation plan header
- Ensure any agent/LLM knows to check current status first
- Create clear documentation hierarchy for handoffs
- Fix markdown formatting issues

This ensures any AI agent or human developer can immediately
understand project state and continue work without confusion.

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

docs/plans/2024-06-22-hostkeeper-implementation.md

@@ -1,5 +1,8 @@
 # Hostkeeper MVP Implementation Plan
 
+> **⚠️ IMPORTANT HANDOFF INSTRUCTIONS**:
+> Before starting implementation, **[check PROJECT_STATE.md](../../PROJECT_STATE.md)** for current progress and what's already been completed. This ensures you're not repeating work or missing dependencies.
+>
 > **For Claude:** REQUIRED SUB-SKILL: Use superpowers:executing-plans to implement this plan task-by-task.
 
 **Goal:** Build a cross-platform SSH/SFTP management tool with secure credential storage, host management, and cross-device sync capabilities through export/import functionality.
@@ -8,6 +11,8 @@
 
 **Tech Stack:** Go 1.21+, Cobra (CLI framework), Bubble Tea (TUI), golang.org/x/crypto/ssh, Viper (config management), JSON/YAML storage
 
+**Current Status**: Planning Complete → Ready for Implementation (Check PROJECT_STATE.md for latest updates)
+
 ---
 
 ## Task 1: Project Setup and Dependencies