fix(docs): use consistent in_progress status naming (GH#444)

Changed all user-facing documentation and help text to use `in_progress`
(underscore) instead of `in-progress` (hyphen) to match the canonical
status value.

Files updated:
- cmd/bd/ready.go - Short description
- cmd/bd/status.go - Long description
- commands/stats.md - Action suggestion
- README.md - Workflow description

Note: CSS class names, HTML IDs, and GitHub label mappings intentionally
kept with hyphens as they follow different conventions.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/ready.go

@@ -12,7 +12,7 @@ import (
 )
 var readyCmd = &cobra.Command{
 	Use:   "ready",
-	Short: "Show ready work (no blockers, open or in-progress)",
+	Short: "Show ready work (no blockers, open or in_progress)",
 	Run: func(cmd *cobra.Command, args []string) {
 		limit, _ := cmd.Flags().GetInt("limit")
 		assignee, _ := cmd.Flags().GetString("assignee")

cmd/bd/status.go

@@ -45,7 +45,7 @@ var statusCmd = &cobra.Command{
 	Short: "Show issue database overview",
 	Long: `Show a quick snapshot of the issue database state.
 
-This command provides a summary of issue counts by state (open, in-progress,
+This command provides a summary of issue counts by state (open, in_progress,
 blocked, closed), ready work, and recent activity over the last 24 hours from git history.
 
 Similar to how 'git status' shows working tree state, 'bd status' gives you