Fix GH#366: Encourage descriptions when creating issues

Addresses GitHub Discussion #366 where users reported Claude Code
creating issues with titles but no descriptions.

Two-pronged solution:

1. Documentation improvements (bd-na8r):
   - Updated AGENTS.md with prominent guidance section
   - Added good/bad examples showing why/what/how to include
   - Updated all bd create examples to include --description
   - Enhanced MCP tool docstring with importance note
   - Updated .github/copilot-instructions.md

2. Code validation (bd-bcrt):
   - Added friendly yellow warning when description is empty
   - Warning skips test issues (title contains "test")
   - Works in both CLI and daemon modes
   - Non-blocking to preserve quick workflows

Evidence from our own projects showed significant empty description
rates:
- ~/src/beads: 110/630 (17.5%)
- ~/wyvern: 8/119 (6.7%)
- ~/src/vc: 3/170 (1.8%)

Fixes bd-0tr0, bd-na8r, bd-bcrt

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

cmd/bd/create.go

@@ -82,6 +82,14 @@ var createCmd = &cobra.Command{
 			description = tmpl.Description
 		}
 
+		// Warn if creating an issue without a description (unless it's a test issue)
+		if description == "" && !strings.Contains(strings.ToLower(title), "test") {
+			yellow := color.New(color.FgYellow).SprintFunc()
+			fmt.Fprintf(os.Stderr, "%s Creating issue without description.\n", yellow("⚠"))
+			fmt.Fprintf(os.Stderr, "  Issues without descriptions lack context for future work.\n")
+			fmt.Fprintf(os.Stderr, "  Consider adding --description=\"Why this issue exists and what needs to be done\"\n")
+		}
+
 		design, _ := cmd.Flags().GetString("design")
 		if design == "" && tmpl != nil {
 			design = tmpl.Design