Add welcome wizard, desktop entry, and Nautilus extension

First-run welcome dialog with skill level and output location setup.
Desktop entry file for GNOME app launcher integration.
Nautilus Python extension with dynamic 'Process with Pixstrip' submenu
that reads both built-in and user presets.

data/live.lashman.Pixstrip.desktop

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+[Desktop Entry]
+Name=Pixstrip
+Comment=Batch image processor - resize, convert, compress, and more
+Exec=pixstrip-gtk %F
+Icon=live.lashman.Pixstrip
+Terminal=false
+Type=Application
+Categories=Graphics;ImageProcessing;
+MimeType=image/jpeg;image/png;image/webp;image/avif;image/gif;image/tiff;image/bmp;
+Keywords=image;photo;resize;convert;compress;batch;metadata;strip;watermark;rename;
+StartupNotify=true

data/nautilus-pixstrip.py

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+"""Nautilus extension for Pixstrip - adds 'Process with Pixstrip' submenu to image context menu."""
+
+import os
+import subprocess
+import json
+
+from gi.repository import Nautilus, GObject
+
+SUPPORTED_MIMETYPES = [
+    "image/jpeg",
+    "image/png",
+    "image/webp",
+    "image/avif",
+    "image/gif",
+    "image/tiff",
+    "image/bmp",
+]
+
+
+def get_presets():
+    """Load built-in and user presets."""
+    presets = [
+        "Blog Photos",
+        "Social Media",
+        "Web Optimization",
+        "Email Friendly",
+        "Privacy Clean",
+        "Photographer Export",
+        "Archive Compress",
+        "Fediverse Ready",
+    ]
+
+    # Load user presets
+    config_dir = os.path.expanduser("~/.config/pixstrip/presets")
+    if os.path.isdir(config_dir):
+        for filename in sorted(os.listdir(config_dir)):
+            if filename.endswith(".json"):
+                filepath = os.path.join(config_dir, filename)
+                try:
+                    with open(filepath) as f:
+                        data = json.load(f)
+                        name = data.get("name", "")
+                        if name and name not in presets:
+                            presets.append(name)
+                except (json.JSONDecodeError, IOError):
+                    pass
+
+    return presets
+
+
+class PixstripMenuProvider(GObject.GObject, Nautilus.MenuProvider):
+    def get_file_items(self, files):
+        # Only show for image files
+        if not files:
+            return []
+
+        for f in files:
+            if f.get_mime_type() not in SUPPORTED_MIMETYPES:
+                return []
+
+        items = []
+
+        # Main menu item
+        top_item = Nautilus.MenuItem(
+            name="PixstripMenuProvider::process",
+            label="Process with Pixstrip",
+            tip="Open images in Pixstrip for batch processing",
+        )
+
+        submenu = Nautilus.Menu()
+        top_item.set_submenu(submenu)
+
+        # Open in Pixstrip
+        open_item = Nautilus.MenuItem(
+            name="PixstripMenuProvider::open",
+            label="Open in Pixstrip...",
+            tip="Open the Pixstrip wizard with these images",
+        )
+        open_item.connect("activate", self._on_open, files)
+        submenu.append_item(open_item)
+
+        # Separator via disabled item
+        sep = Nautilus.MenuItem(
+            name="PixstripMenuProvider::sep1",
+            label="---",
+            sensitive=False,
+        )
+        submenu.append_item(sep)
+
+        # Preset items
+        for preset in get_presets():
+            safe_name = preset.replace(" ", "_").lower()
+            item = Nautilus.MenuItem(
+                name=f"PixstripMenuProvider::preset_{safe_name}",
+                label=preset,
+                tip=f"Process with {preset} preset",
+            )
+            item.connect("activate", self._on_preset, files, preset)
+            submenu.append_item(item)
+
+        items.append(top_item)
+        return items
+
+    def _on_open(self, menu, files):
+        paths = [f.get_location().get_path() for f in files]
+        subprocess.Popen(["pixstrip-gtk"] + paths)
+
+    def _on_preset(self, menu, files, preset):
+        paths = [f.get_location().get_path() for f in files]
+        subprocess.Popen(
+            ["pixstrip-cli", "process"] + paths + ["--preset", preset]
+        )