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/info.go

@@ -292,6 +292,7 @@ var versionChanges = []VersionChange{
 		Version: "0.37.0",
 		Date:    "2025-12-26",
 		Changes: []string{
+			"BREAKING: Ephemeral API rename (bd-o18s) - Wisp→Ephemeral: JSON 'wisp'→'ephemeral', bd wisp→bd ephemeral",
 			"NEW: bd gate create/show/list/close/wait (bd-udsi) - Async coordination primitives for agent workflows",
 			"NEW: bd gate eval (gt-twjr5.2) - Evaluate timer gates and GitHub gates (gh:run, gh:pr, mail)",
 			"NEW: bd gate approve (gt-twjr5.4) - Human gate approval command",