Replace 'gastown' with 'greenplace' in user-facing docs/examples

Using "greenplace" (The Green Place from Mad Max: Fury Road) as the
canonical example project/rig name in documentation and help text.
This provides a clearer distinction from the actual gastown repo name.

Changes:
- docs/*.md: Updated all example paths and commands
- internal/cmd/*.go: Updated help text examples
- internal/templates/: Updated example references
- Tests: Updated to use greenplace in example session names

Note: Import paths (github.com/steveyegge/gastown) and actual code
paths referencing the gastown repo structure are unchanged.

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

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

internal/cmd/activity.go

@@ -56,16 +56,16 @@ Supported event types for refinery:
   queue_processed  - When refinery finishes processing queue
 
 Common options:
-  --actor    Who is emitting the event (e.g., gastown/witness)
+  --actor    Who is emitting the event (e.g., greenplace/witness)
   --rig      Which rig the event is about
   --message  Human-readable message
 
 Examples:
-  gt activity emit patrol_started --rig gastown --count 3
-  gt activity emit polecat_checked --rig gastown --polecat Toast --status working --issue gt-xyz
-  gt activity emit polecat_nudged --rig gastown --polecat Toast --reason "idle for 10 minutes"
-  gt activity emit escalation_sent --rig gastown --target Toast --to mayor --reason "unresponsive"
-  gt activity emit patrol_complete --rig gastown --count 3 --message "All polecats healthy"`,
+  gt activity emit patrol_started --rig greenplace --count 3
+  gt activity emit polecat_checked --rig greenplace --polecat Toast --status working --issue gp-xyz
+  gt activity emit polecat_nudged --rig greenplace --polecat Toast --reason "idle for 10 minutes"
+  gt activity emit escalation_sent --rig greenplace --target Toast --to mayor --reason "unresponsive"
+  gt activity emit patrol_complete --rig greenplace --count 3 --message "All polecats healthy"`,
 	Args: cobra.ExactArgs(1),
 	RunE: runActivityEmit,
 }