docs: Document multi-repo workflow with global daemon

Implements bd-122: Document how to use beads across multiple projects

Added comprehensive multi-repo documentation:
- README.md: Global daemon section with architecture diagram
- AGENTS.md: MCP multi-repo configuration (global daemon + per-project)
- integrations/beads-mcp/README.md: BEADS_WORKING_DIR usage
- Mermaid diagram showing one daemon serving multiple repos

Documentation covers:
- Global daemon (bd daemon --global) for system-wide usage
- Per-project MCP instances with BEADS_WORKING_DIR
- Comparison table (local vs global)
- When to use each approach
- Example workflows for multi-project setups

Benefits of global daemon:
- One daemon process for all repos
- Automatic socket discovery (local -> global fallback)
- Better resource usage
- Per-request context routing to correct database

Amp-Thread-ID: https://ampcode.com/threads/T-ea606216-b886-4af0-bba8-56d000362d01
Co-authored-by: Amp <amp@ampcode.com>

README.md

@@ -916,6 +916,7 @@ bd daemon --auto-push                 # Auto-push commits (requires auto-commit)
 bd daemon --log /var/log/bd.log       # Custom log file path
 bd daemon --status                    # Show daemon status
 bd daemon --stop                      # Stop running daemon
+bd daemon --global                    # Run as global daemon (see below)
 ```
 
 The daemon is ideal for:
@@ -926,6 +927,104 @@ The daemon is ideal for:
 
 The daemon gracefully shuts down on SIGTERM and maintains a PID file at `.beads/daemon.pid` for process management.
 
+#### Global Daemon for Multiple Projects
+
+**New in v0.9.11:** Run a single daemon to serve all your projects system-wide:
+
+```bash
+# Start global daemon (serves all repos)
+bd daemon --global
+
+# Check global daemon status
+bd daemon --status --global
+
+# Stop global daemon
+bd daemon --stop --global
+```
+
+**Local vs Global Daemon:**
+
+| Mode | Socket Location | Use Case |
+|------|----------------|----------|
+| **Local** (default) | `.beads/bd.sock` | Single project, per-repo daemon |
+| **Global** (`--global`) | `~/.beads/bd.sock` | Multiple projects, system-wide daemon |
+
+**When to use global daemon:**
+- ✅ Working on multiple beads-enabled projects
+- ✅ Want one daemon process for all repos
+- ✅ Better resource usage (one daemon vs many)
+- ✅ Automatic fallback for CLI commands
+
+**How it works:**
+1. Global daemon creates socket at `~/.beads/bd.sock`
+2. CLI commands check local socket first, then fall back to global
+3. Daemon serves requests from any repository
+4. Each repo still has its own database at `.beads/*.db`
+
+**Architecture:**
+```mermaid
+graph TB
+    subgraph "Global Daemon Setup"
+        GD[bd daemon --global<br/>~/.beads/bd.sock]
+        
+        subgraph "Project 1: webapp"
+            P1DB[.beads/webapp.db]
+            P1JSON[.beads/issues.jsonl]
+        end
+        
+        subgraph "Project 2: api"
+            P2DB[.beads/api.db]
+            P2JSON[.beads/issues.jsonl]
+        end
+        
+        subgraph "Project 3: docs"
+            P3DB[.beads/docs.db]
+            P3JSON[.beads/issues.jsonl]
+        end
+        
+        MCP[MCP Server<br/>beads-mcp]
+        CLI[CLI Commands<br/>bd ready, bd create, etc.]
+        
+        MCP -->|Unix Socket| GD
+        CLI -->|Unix Socket| GD
+        
+        GD -->|cwd: ~/projects/webapp| P1DB
+        GD -->|cwd: ~/projects/api| P2DB
+        GD -->|cwd: ~/projects/docs| P3DB
+        
+        P1DB -.->|export| P1JSON
+        P2DB -.->|export| P2JSON
+        P3DB -.->|export| P3JSON
+    end
+    
+    style GD fill:#1a1a2e,stroke:#16c5c5,stroke-width:3px,color:#fff
+    style MCP fill:#0f3460,stroke:#16c5c5,stroke-width:2px,color:#fff
+    style CLI fill:#0f3460,stroke:#16c5c5,stroke-width:2px,color:#fff
+    style P1DB fill:#16213e,stroke:#16c5c5,color:#fff
+    style P2DB fill:#16213e,stroke:#16c5c5,color:#fff
+    style P3DB fill:#16213e,stroke:#16c5c5,color:#fff
+    style P1JSON fill:#16213e,stroke:#e94560,color:#fff
+    style P2JSON fill:#16213e,stroke:#e94560,color:#fff
+    style P3JSON fill:#16213e,stroke:#e94560,color:#fff
+```
+
+**Example: Multi-repo workflow**
+```bash
+# Start global daemon once
+bd daemon --global --auto-commit --auto-push
+
+# Work on different projects - daemon handles all of them
+cd ~/projects/webapp && bd create "Fix navigation bug" -p 1
+cd ~/projects/api && bd create "Add rate limiting" -p 1
+cd ~/projects/docs && bd create "Update API guide" -p 2
+
+# All commands use the same global daemon automatically
+cd ~/projects/webapp && bd ready     # Uses global daemon
+cd ~/projects/api && bd ready         # Uses global daemon
+```
+
+**Note:** Global daemon doesn't require git repos, making it suitable for non-git projects or multi-repo setups.
+
 ### Optional: Git Hooks for Immediate Sync
 
 Create `.git/hooks/pre-commit`:
@@ -1039,6 +1138,7 @@ Each project gets its own `.beads/` directory with its own database and JSONL fi
 - Multiple agents working on different projects simultaneously → No conflicts
 - Same machine, different repos → Each finds its own `.beads/*.db` automatically
 - Agents in subdirectories → bd walks up to find the project root (like git)
+- **Global daemon** → One daemon process serves all projects (v0.9.11+)
 
 **Limitation:** Issues cannot reference issues in other projects. Each database is isolated by design. If you need cross-project tracking, initialize bd in a parent directory that contains both projects.
 
@@ -1053,6 +1153,8 @@ cd ~/work/api && bd ready --json       # Uses ~/work/api/.beads/api.db
 # No conflicts! Completely isolated databases.
 ```
 
+**Recommended for multi-project setups:** Use the global daemon (`bd daemon --global`) to serve all projects with a single daemon process. See [Global Daemon for Multiple Projects](#global-daemon-for-multiple-projects) above.
+
 ### How do I migrate from GitHub Issues / Jira / Linear?
 
 We don't have automated migration tools yet, but you can: