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/session.go

@@ -120,7 +120,7 @@ This command is a low-level primitive for file-based injection or
 cases where you need raw tmux send-keys behavior.
 
 Examples:
-  gt nudge gastown/furiosa "Check your mail"     # Preferred
+  gt nudge greenplace/furiosa "Check your mail"     # Preferred
   gt session inject wyvern/Toast -f prompt.txt   # For file injection`,
 	Args: cobra.ExactArgs(1),
 	RunE: runSessionInject,
@@ -160,7 +160,7 @@ Use this for manual health checks or debugging session issues.
 
 Examples:
   gt session check              # Check all rigs
-  gt session check gastown      # Check specific rig`,
+  gt session check greenplace      # Check specific rig`,
 	Args: cobra.MaximumNArgs(1),
 	RunE: runSessionCheck,
 }