#15909: Guard notifications on macOS; fix focus issue and build fixes

Fixes https://github.com/openclaw/openclaw/issues/15911 Some build fixes and version updates for a smoother dev setup on macOS - PermissionManager: add canAccessNotificationCenter() and avoid calling UNUserNotificationCenter when the app has no bundle identifier - make ensureCapability return boolean results and propagate them; - add macOS-specific handling to exclude .ephemeral authorization (accept .authorized/.provisional on macOS) and mirror that behavior in the batch capability checks. - ChatComposer: defer clearing shouldFocus with DispatchQueue.main.async to avoid mutating state while making the text view first responder (fixes a focus/race issue). - Package.swift: add a macOS-only comment and update the platforms list to include macOS v15 and iOS v18. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Improved macOS notification handling and fixed a SwiftUI state mutation race condition. The PR guards `UNUserNotificationCenter` access with a bundle identifier check (apps without bundle IDs can't use the notification center), excludes `.ephemeral` authorization status on macOS (iOS-only), updates platform requirements to include iOS v18 for shared dependency compatibility, and defers `shouldFocus` state clearing with `DispatchQueue.main.async` to prevent mutating state during view updates. Key changes: - Added `canAccessNotificationCenter()` guard to prevent crashes when bundle identifier is nil - Made `ensureCapability()` return boolean results for proper error propagation - Platform-specific handling: `.ephemeral` excluded on macOS, only `.authorized` and `.provisional` accepted - Fixed ChatComposer focus race by deferring state mutation to next run loop - Updated Package.swift platforms to include iOS v18 (needed for OpenClawKit shared dependency) <h3>Confidence Score: 4/5</h3> - This PR is safe to merge with minimal risk - the changes are defensive improvements - The changes are well-scoped defensive improvements (guard clauses, platform-specific handling, async state mutation fix). All changes follow established Swift/SwiftUI patterns and address real edge cases. The only minor issue is a potentially confusing comment in Package.swift where the file states it's macOS-only but includes iOS platform - this is for dependency compatibility but could be clearer. - No files require special attention _{Last reviewed commit: e3d2b12} <!-- greptile_other_comments_section --> _{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!} <!-- /greptile_comment -->