Add architecture and project plan documentation

ARCHITECTURE.md covers the system design: exod backend, single Kotlin
desktop app (Obsidian-style), layered architecture, data flow, CAS blob
store, cross-pillar integration, and key design decisions.

PROJECT_PLAN.md defines six implementation phases from foundation through
remote access, with concrete deliverables per phase.

CLAUDE.md updated to reference both documents and reflect the single-app
UI decision with unified search.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -6,7 +6,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 **kExocortex** is a personal knowledge management system — an "exocortex" for capturing, organizing, and retrieving knowledge. It combines two pillars: an **artifact repository** (for storing source documents like PDFs, papers, webpages) and a **knowledge graph** (for linking notes and ideas).
 
-The project is in active design and early implementation. The design docs in `docs/` are the primary working material.
+The project is in active design and early implementation. See `ARCHITECTURE.md` for the technical system design and `PROJECT_PLAN.md` for the phased implementation plan.
 
 ## Repository Structure
 
@@ -38,7 +38,7 @@ The system design calls for:
 3. Local blob store (content-addressable)
 4. Remote Minio backup for blobs
 5. Reverse-proxy frontend over Tailscale for remote/mobile access
-6. Kotlin desktop apps covering four UI facets: query, exploration, presentation, and update
+6. Single Kotlin desktop app (Obsidian-style layout) with tree sidebar, contextual main panel, graph view, and unified search with selector prefixes
 
 ## Git Remote