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/start.go

@@ -89,12 +89,12 @@ var startCrewCmd = &cobra.Command{
 This is a convenience command that combines 'gt crew add' and 'gt crew at --detached'.
 The crew session starts in the background with Claude running and ready.
 
-The name can include the rig in slash format (e.g., gastown/joe).
+The name can include the rig in slash format (e.g., greenplace/joe).
 If not specified, the rig is inferred from the current directory.
 
 Examples:
   gt start crew joe                    # Start joe in current rig
-  gt start crew gastown/joe            # Start joe in gastown rig
+  gt start crew greenplace/joe            # Start joe in gastown rig
   gt start crew joe --rig beads        # Start joe in beads rig`,
 	Args: cobra.ExactArgs(1),
 	RunE: runStartCrew,
@@ -660,7 +660,7 @@ func cleanupPolecats(townRoot string) {
 func runStartCrew(cmd *cobra.Command, args []string) error {
 	name := args[0]
 
-	// Parse rig/name format (e.g., "gastown/joe" -> rig=gastown, name=joe)
+	// Parse rig/name format (e.g., "greenplace/joe" -> rig=gastown, name=joe)
 	rigName := startCrewRig
 	if parsedRig, crewName, ok := parseRigSlashName(name); ok {
 		if rigName == "" {