feat: Rename 'wisp' to 'ephemeral' in beads API (bd-o18s)

BREAKING CHANGE: API field and CLI command renamed

- types.Issue.Wisp → types.Issue.Ephemeral
- JSON field: "wisp" → "ephemeral"
- CLI: bd wisp → bd ephemeral
- Flags: --wisp → --ephemeral
- ID prefix: wisp → eph

The SQLite column already uses 'ephemeral' so no schema migration needed.

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

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

cmd/bd/hook.go

@@ -87,8 +87,8 @@ func runHook(cmd *cobra.Command, args []string) {
 
 	for _, issue := range issues {
 		phase := "mol"
-		if issue.Wisp {
-			phase = "wisp"
+		if issue.Ephemeral {
+			phase = "ephemeral"
 		}
 		fmt.Printf("  📌 %s (%s) - %s\n", issue.ID, phase, issue.Status)
 		fmt.Printf("     %s\n", issue.Title)