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>

docs/MOLECULES.md

@@ -129,7 +129,7 @@ For reusable workflows, beads uses a chemistry metaphor:
 
 ```bash
 bd pour <proto>                  # Proto → Mol (persistent instance)
-bd wisp create <proto>           # Proto → Wisp (ephemeral instance)
+bd ephemeral create <proto>           # Proto → Wisp (ephemeral instance)
 bd mol squash <id>               # Mol/Wisp → Digest (permanent record)
 bd mol burn <id>                 # Wisp → nothing (discard)
 ```
@@ -227,10 +227,10 @@ bd close <id> --reason "Done"
 Wisps accumulate if not squashed/burned:
 
 ```bash
-bd wisp list           # Check for orphans
+bd ephemeral list           # Check for orphans
 bd mol squash <id>     # Create digest
 bd mol burn <id>       # Or discard
-bd wisp gc             # Garbage collect old wisps
+bd ephemeral gc             # Garbage collect old wisps
 ```
 
 ## Layer Cake Architecture
@@ -273,7 +273,7 @@ bd dep tree <id>                 # Show dependency tree
 
 ```bash
 bd pour <proto> --var k=v        # Template → persistent mol
-bd wisp create <proto>           # Template → ephemeral wisp
+bd ephemeral create <proto>           # Template → ephemeral wisp
 bd mol bond A B                  # Connect work graphs
 bd mol squash <id>               # Compress to digest
 bd mol burn <id>                 # Discard without record