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/gate.go

@@ -157,7 +157,7 @@ Examples:
 				Status:    types.StatusOpen,
 				Priority:  1, // Gates are typically high priority
 				// Assignee left empty - orchestrator decides who processes gates
-				Wisp:      true, // Gates are wisps (ephemeral)
+				Ephemeral:      true, // Gates are wisps (ephemeral)
 				AwaitType: awaitType,
 				AwaitID:   awaitID,
 				Timeout:   timeout,