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-town-root-detection.patch

@@ -0,0 +1,19 @@
+diff --git a/internal/cmd/prime.go b/internal/cmd/prime.go
+index 0000000..1111111 100644
+--- a/internal/cmd/prime.go
++++ b/internal/cmd/prime.go
+@@ -276,12 +276,12 @@ func detectRole(cwd, townRoot string) RoleInfo {
+
+ 	// Check for mayor role
+ 	// At town root, or in mayor/ or mayor/rig/
+ 	if relPath == "." || relPath == "" {
+-		ctx.Role = RoleMayor
+-		return ctx
++		return ctx // RoleUnknown - town root is shared space
+ 	}
++
++	// Check for mayor role: mayor/ or mayor/rig/
+ 	if len(parts) >= 1 && parts[0] == "mayor" {
+ 		ctx.Role = RoleMayor
+ 		return ctx
+ 	}