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>

integrations/beads-mcp/src/beads_mcp/tools.py

@@ -362,6 +362,13 @@ async def beads_create_issue(
 ) -> Issue:
     """Create a new issue.
 
+    IMPORTANT: Always provide a meaningful description with context about:
+    - Why this issue exists (problem statement or need)
+    - What needs to be done (scope and approach)
+    - How you discovered it (if applicable)
+
+    Issues without descriptions lack context for future work and make prioritization difficult.
+
     Use this when you discover new work during your session.
     Link it back with beads_add_dependency using 'discovered-from' type.
     """