First-run chooser, node shutdown on switch, file picker, export path fix

- First-run: show Start Fresh / Import chooser only when single auto-created
  identity with no profile (not on every boot without a display name).
- Identity switch: shut down old node's endpoint before starting new one.
  Fixes lockup after multiple switches (zombie background tasks).
- File picker: native Browse buttons on export (folder) and import (ZIP file)
  via tauri-plugin-dialog.
- Export path: resolve relative paths against home dir (was using process cwd).
- Lightbox close: only close on overlay/image click, not inner form content.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -2780,6 +2780,7 @@ dependencies = [
  "serde_json",
  "tauri",
  "tauri-build",
+ "tauri-plugin-dialog",
  "tauri-plugin-notification",
  "tokio",
  "tracing",
@@ -4632,6 +4633,30 @@ version = "0.7.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1e061d1b48cb8d38042de4ae0a7a6401009d6143dc80d2e2d6f31f0bdd6470c7"
 
+[[package]]
+name = "rfd"
+version = "0.16.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a15ad77d9e70a92437d8f74c35d99b4e4691128df018833e99f90bcd36152672"
+dependencies = [
+ "block2",
+ "dispatch2",
+ "glib-sys",
+ "gobject-sys",
+ "gtk-sys",
+ "js-sys",
+ "log",
+ "objc2",
+ "objc2-app-kit",
+ "objc2-core-foundation",
+ "objc2-foundation",
+ "raw-window-handle",
+ "wasm-bindgen",
+ "wasm-bindgen-futures",
+ "web-sys",
+ "windows-sys 0.60.2",
+]
+
 [[package]]
 name = "ring"
 version = "0.17.14"
@@ -5598,6 +5623,48 @@ dependencies = [
  "walkdir",
 ]
 
+[[package]]
+name = "tauri-plugin-dialog"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1fa4150c95ae391946cc8b8f905ab14797427caba3a8a2f79628e956da91809"
+dependencies = [
+ "log",
+ "raw-window-handle",
+ "rfd",
+ "serde",
+ "serde_json",
+ "tauri",
+ "tauri-plugin",
+ "tauri-plugin-fs",
+ "thiserror 2.0.18",
+ "url",
+]
+
+[[package]]
+name = "tauri-plugin-fs"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "36e1ec28b79f3d0683f4507e1615c36292c0ea6716668770d4396b9b39871ed8"
+dependencies = [
+ "anyhow",
+ "dunce",
+ "glob",
+ "log",
+ "objc2-foundation",
+ "percent-encoding",
+ "schemars 0.8.22",
+ "serde",
+ "serde_json",
+ "serde_repr",
+ "tauri",
+ "tauri-plugin",
+ "tauri-utils",
+ "thiserror 2.0.18",
+ "toml 0.9.11+spec-1.1.0",
+ "url",
+]
+
 [[package]]
 name = "tauri-plugin-notification"
 version = "2.3.3"