refactor(development): move gastown patches to separate files

Replace inline postPatch substituteInPlace calls with proper unified
diff patch files, following the pattern established by beads.

This improves maintainability:
- Each patch is in its own file with clear naming
- Patches use proper unified diff format
- Easier to review, update, and track individual fixes
- Default.nix is cleaner (237 lines of substituteInPlace -> 15 lines)

Patches included:
- gastown-fix-validate-recipient.patch
- gastown-fix-agent-bead-address-title.patch
- gastown-fix-agent-bead-rig-prefix.patch
- gastown-fix-role-home-paths.patch
- gastown-fix-town-root-detection.patch
- gastown-fix-copydir-symlinks.patch
- gastown-statusline-optimization.patch

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

home/roles/development/gastown-fix-role-home-paths.patch

@@ -0,0 +1,19 @@
+diff --git a/internal/cmd/role.go b/internal/cmd/role.go
+index 0000000..1111111 100644
+--- a/internal/cmd/role.go
++++ b/internal/cmd/role.go
+@@ -326,11 +326,11 @@ func getRoleHome(role Role, rig, polecat, townRoot string) string {
+ 		if rig == "" || polecat == "" {
+ 			return ""
+ 		}
+-		return filepath.Join(townRoot, rig, "polecats", polecat, "rig")
++		return filepath.Join(townRoot, rig, "polecats", polecat)
+ 	case RoleCrew:
+ 		if rig == "" || polecat == "" {
+ 			return ""
+ 		}
+-		return filepath.Join(townRoot, rig, "crew", polecat, "rig")
++		return filepath.Join(townRoot, rig, "crew", polecat)
+ 	default:
+ 		return ""
+ 	}