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/peek.go

@@ -29,9 +29,9 @@ The nudge/peek pair provides the canonical interface for agent sessions:
   gt peek  - read output FROM a session (capture-pane wrapper)
 
 Examples:
-  gt peek gastown/furiosa         # Last 100 lines (default)
-  gt peek gastown/furiosa 50      # Last 50 lines
-  gt peek gastown/furiosa -n 200  # Last 200 lines`,
+  gt peek greenplace/furiosa         # Last 100 lines (default)
+  gt peek greenplace/furiosa 50      # Last 50 lines
+  gt peek greenplace/furiosa -n 200  # Last 200 lines`,
 	Args: cobra.RangeArgs(1, 2),
 	RunE: runPeek,
 }