Rename ephemeral -> wisp terminology throughout Gas Town

- .beads-ephemeral/ -> .beads-wisp/
- Rename doctor checks: EphemeralCheck -> WispCheck
- Update all docs to use 'transient' for polecats, 'wisp' for molecules
- Preserve 'ephemeral' only as descriptive adjective for wisps
- Steam engine metaphor: wisps are steam vapors that dissipate

Part of Christmas launch wisp terminology unification.

internal/templates/roles/crew.md.tmpl

@@ -5,7 +5,7 @@
 ## Your Role: CREW WORKER ({{ .Polecat }} in {{ .RigName }})
 
 You are a **crew worker** - the overseer's (human's) personal workspace within the
-{{ .RigName }} rig. Unlike polecats which are witness-managed and ephemeral, you are:
+{{ .RigName }} rig. Unlike polecats which are witness-managed and transient, you are:
 
 - **Persistent**: Your workspace is never auto-garbage-collected
 - **User-managed**: The overseer controls your lifecycle, not the Witness
@@ -26,7 +26,7 @@ Town ({{ .TownRoot }})
 │   ├── .beads/     ← Issue tracking (you have write access)
 │   ├── crew/
 │   │   └── {{ .Polecat }}/   ← You are here (your git clone)
-│   ├── polecats/   ← Ephemeral workers (not you)
+│   ├── polecats/   ← Transient workers (not you)
 │   ├── refinery/   ← Merge queue processor
 │   └── witness/    ← Polecat lifecycle (doesn't monitor you)
 ```
@@ -141,7 +141,7 @@ Before ending your session:
 
 ## Tips
 
-- **You own your workspace**: Unlike polecats, you're not ephemeral. Keep it organized.
+- **You own your workspace**: Unlike polecats, you're not transient. Keep it organized.
 - **Handoff liberally**: When in doubt, write a handoff mail. Context is precious.
 - **Stay in sync**: Pull from upstream regularly to avoid merge conflicts.
 - **Ask for help**: No Witness means no automatic escalation. Reach out proactively.