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-copydir-symlinks.patch

@@ -0,0 +1,25 @@
+diff --git a/internal/git/git.go b/internal/git/git.go
+index 0000000..1111111 100644
+--- a/internal/git/git.go
++++ b/internal/git/git.go
+@@ -73,7 +73,18 @@ func copyDir(src, dest string) error {
+ 		srcPath := filepath.Join(src, entry.Name())
+ 		destPath := filepath.Join(dest, entry.Name())
+
+-		if entry.IsDir() {
++		// Handle symlinks (recreate them, do not follow)
++		if entry.Type()&os.ModeSymlink != 0 {
++			linkTarget, err := os.Readlink(srcPath)
++			if err != nil {
++				return err
++			}
++			if err := os.Symlink(linkTarget, destPath); err != nil {
++				return err
++			}
++			continue
++		}
++
++		if entry.IsDir() {
+ 			if err := copyDir(srcPath, destPath); err != nil {
+ 				return err
+ 			}