Replace gt rigs with gt rig list in templates and docs (#217)

The command was renamed from `gt rigs` to `gt rig` with subcommands.
This updates all references to use `gt rig list` for listing rigs.

internal/formula/formulas/mol-digest-generate.formula.toml

@@ -78,7 +78,7 @@ Gather activity data from each rig in the town.
 
 **1. List accessible rigs:**
 ```bash
-gt rigs
+gt rig list
 # Returns list of rigs: gastown, beads, etc.
 ```
 

internal/formula/formulas/mol-orphan-scan.formula.toml

@@ -57,7 +57,7 @@ gt hook               # Shows scope in hook_bead
 
 ```bash
 # If town-wide
-gt rigs                     # Get list of all rigs
+gt rig list                 # Get list of all rigs
 
 # If specific rig
 # Just use that rig

internal/formula/formulas/mol-town-shutdown.formula.toml

@@ -85,7 +85,7 @@ Archive and clear all agent inboxes across all rigs.
 
 ```bash
 # For each rig
-for rig in $(gt rigs --names); do
+for rig in $(gt rig list --names); do
   gt mail clear $rig/witness --archive
   gt mail clear $rig/refinery --archive
 done