Add Dynamic Island Live Activity for chat streaming

[zmanian]

Summary

ActivityKit Live Activity shows Claude's progress in the Dynamic Island and on the Lock Screen while the app is backgrounded. Inspired by Chowder-iOS.

• Dynamic Island compact: Colored status dot (blue = active, green = done) and current intent text
• Dynamic Island expanded: Sprite name, current tool, step count, and previously completed tool
• Lock Screen banner: Intent card stack with depth effect and live timer
• Payload safety: Truncate userTask (200 chars) and intent strings (100 chars) to stay under ActivityKit's 4KB limit
• Diagnostics: Surface startActivity failures via return value and lastError property, log with activity IDs

Note: This PR is stacked on #7 (thinking shimmer) because it uses activityLabel from ToolUseCard. Merge #7 first.

New files

• Wisp/Models/WispActivityAttributes.swift -- shared ActivityKit attributes model
• Wisp/Services/LiveActivityManager.swift -- singleton managing Activity lifecycle with debounced updates
• WispActivityWidget/WispLiveActivity.swift -- Dynamic Island compact/expanded + Lock Screen banner views
• WispActivityWidget/WispActivityWidgetBundle.swift -- widget bundle entry point
• WispActivityWidget/Info.plist -- NSExtension configuration for WidgetKit
• Wisp/Wisp.entitlements, WispActivityWidget/WispActivityWidget.entitlements -- entitlements

Modified files

• Wisp/ViewModels/ChatViewModel.swift -- hooks for Live Activity start/update/end tied to NDJSON event flow
• Wisp.xcodeproj/project.pbxproj -- WispActivityWidget extension target, embed phase, NSSupportsLiveActivities

Test plan

• Build succeeds for both Wisp and WispActivityWidget targets
• All existing tests pass
• Send a tool-using prompt -- verify Dynamic Island shows status dot + current intent
• Verify Lock Screen banner shows sprite name, intent cards with depth effect, live timer
• Verify activity ends with green checkmark when Claude responds with text
• Verify activity dismisses after ~8 seconds on completion
• Test with long prompts (>200 chars) -- should truncate without crashing

Generated with Claude Code

[mcintyre94]

Thanks, this is really cool! I'm going to hold off on merging it for now because I want to think a bit more about how I'd like this to work with multiple chats which is how I'm often using Wisp.

[zmanian]

The current thing has its flaws. Happy to brainstorm improving it.

[mcintyre94]

Some not-super-well-organised thoughts:

• Apparently iOS does handle multiple activities for a single app well, so that's not a blocker
• I really like dynamic island as a UI and want it for Wisp!
• I think it makes sense to ship this after we have notifications for the 'Done' status, so we can complete tasks in the dynamic island when the app is backgrounded. Would link well with notifications for that
• When the app is foregrounded we can do much richer updates based on streaming tool use. But our notification system won't handle that granularity (ie no tool use hook) because it gets into data I don't want people sending to my server
• We now have automatic chat naming, which should make this more useful