Add bd info command to show database path and daemon status

Implements bd-145. Users can now easily determine which database file bd is using
and check daemon connection status.

Features:
- Shows absolute database path
- Displays daemon status (connected/mode/health/version)
- Shows issue count
- Supports --json output for programmatic use
- Works in both daemon and direct modes

Example output:
  bd info                    # Human-readable
  bd info --json             # JSON for agents
  bd info --no-daemon        # Force direct mode

Updated documentation in README.md and AGENTS.md.

Amp-Thread-ID: https://ampcode.com/threads/T-a33c0762-f800-4fea-9510-6a803d8aece8
Co-authored-by: Amp <amp@ampcode.com>

README.md

@@ -174,6 +174,7 @@ Options:
 ### Viewing Issues
 
 ```bash
+bd info                                    # Show database path and daemon status
 bd show bd-1                               # Show full details
 bd list                                    # List all issues
 bd list --status open                      # Filter by status
@@ -183,6 +184,7 @@ bd list --label=backend,urgent             # Filter by labels (AND)
 bd list --label-any=frontend,backend       # Filter by labels (OR)
 
 # JSON output for agents
+bd info --json
 bd list --json
 bd show bd-1 --json
 ```