feat(webshell): neues Library-Product ManaWebShell (v0.6.0)

WKWebView-Huelle fuer Hybrid-Apps (Web-Lese-Surfaces + native
Submit/Widget/ShareExt). Extrahiert aus den fast-byte-identischen
`WebShell/`-Ordnern in seepuls-native und zitare-native (~900 LOC,
davon ~700 LOC Duplikat). Audit 2026-05-17 V2.

Neu (public API):
- `WebShellView` — WKWebView-Wrapper mit Progress-Bar, Pull-to-
  Refresh (iOS), Fehler-Snackbar, External-Link-Delegation. Universal
  (iOS + macOS)
- `WebShellConfig` — Host-Whitelist mit Wildcard-Support (`"*.mana.how"`),
  User-Agent, Theme-Hints, User-Scripts
- `WebTarget` — URL + monoton wachsender reloadToken
- `WebNavState` — @Observable, @MainActor, reaktiver Nav-State
- `WebShellCoordinator` — WKNavigationDelegate + WKUIDelegate
- `WebShellScripts` — Helfer fuer `preferDarkScheme`,
  `syncDarkMode(localStorageKey:)`, `hideElements(selectors:tagName:)`

Logging unter Subsystem `ev.mana.webshell` (App-OSLog bleibt eigen).

Tests: 6 neue Tests gegen `WebShellConfig.isAllowed` (Wildcards,
Negativ-Cases). 50/50 grün insgesamt (6 ManaWebShell + 44 ManaAuthUI).

Doku: `mana/docs/playbooks/HYBRID_NATIVE_APP.md` (Schwester-Repo).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Sources/ManaWebShell/WebNavState.swift

@@ -0,0 +1,16 @@
+import Foundation
+
+/// Reactive Navigation-State, geteilt zwischen SwiftUI und Coordinator.
+/// Auf `MainActor` — alle Mutationen passieren via WKWebView-Callbacks
+/// (KVO + Delegate), die WebKit auf Main liefert.
+@Observable
+@MainActor
+public final class WebNavState {
+    public var isLoading: Bool = false
+    public var estimatedProgress: Double = 0
+    public var lastError: String?
+    public var currentURL: URL?
+    public var canGoBack: Bool = false
+
+    public init() {}
+}