Add Projects: third tab, swipe-to-file, per-project note capture

Notes gain an optional project (schema v4, additive). Projects derive
from note values like tags — no separate entity. Tab naming
(Projects/Categories) is a Settings choice applied across the UI.

Claude-Session: https://claude.ai/code/session_014esDWi42URLEC6Cj17hGQ3

Notes/Views/App/ContentView.swift

@@ -3,6 +3,9 @@ import SwiftUI
 struct ContentView: View {
     @Environment(SyncEngine.self) private var syncEngine
 
+    @AppStorage(ProjectsNaming.storageKey) private var namingRaw = ProjectsNaming.projects.rawValue
+    private var naming: ProjectsNaming { ProjectsNaming(rawValue: namingRaw) ?? .projects }
+
     var body: some View {
         if syncEngine.iCloudStatus == .unavailable {
             ICloudGateView()
@@ -16,6 +19,10 @@ struct ContentView: View {
                     TagsView()
                 }
 
+                Tab(naming.plural, systemImage: "folder") {
+                    ProjectsView()
+                }
+
                 Tab("Settings", systemImage: "gearshape") {
                     SettingsView()
                 }