refactor: rename Ephemeral → Wisp (Steam Engine metaphor)

Wisp = ephemeral vapor produced by the Steam Engine (Gas Town).
This aligns with the metaphor:
- Claude = Fire
- Claude Code = Steam
- Gas Town = Steam Engine
- Wisps = ephemeral vapor it produces

Changes:
- types.Issue.Ephemeral → types.Issue.Wisp
- types.IssueFilter.Ephemeral → types.IssueFilter.Wisp
- JSON field: "ephemeral" → "wisp"
- CLI flag: --ephemeral → --wisp (bd cleanup)
- All tests updated

Note: SQLite column remains "ephemeral" (no migration needed).
This is a breaking change for JSON consumers using 0.33.0.

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

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

internal/types/types.go

@@ -41,8 +41,8 @@ type Issue struct {
 	OriginalType string     `json:"original_type,omitempty"` // Issue type before deletion (for tombstones)
 
 	// Messaging fields (bd-kwro): inter-agent communication support
-	Sender    string `json:"sender,omitempty"`    // Who sent this (for messages)
-	Ephemeral bool   `json:"ephemeral,omitempty"` // Can be bulk-deleted when closed
+	Sender string `json:"sender,omitempty"` // Who sent this (for messages)
+	Wisp   bool   `json:"wisp,omitempty"`   // Wisp = ephemeral vapor from the Steam Engine; bulk-deleted when closed
 	// NOTE: RepliesTo, RelatesTo, DuplicateOf, SupersededBy moved to dependencies table
 	// per Decision 004 (Edge Schema Consolidation). Use dependency API instead.
 
@@ -484,8 +484,8 @@ type IssueFilter struct {
 	// Tombstone filtering (bd-1bu)
 	IncludeTombstones bool // If false (default), exclude tombstones from results
 
-	// Ephemeral filtering (bd-kwro.9)
-	Ephemeral *bool // Filter by ephemeral flag (nil = any, true = only ephemeral, false = only non-ephemeral)
+	// Wisp filtering (bd-kwro.9)
+	Wisp *bool // Filter by wisp flag (nil = any, true = only wisps, false = only non-wisps)
 
 	// Pinned filtering (bd-7h5)
 	Pinned *bool // Filter by pinned flag (nil = any, true = only pinned, false = only non-pinned)