fix: activity name being ignored when starting live activity

[rshallam]

Fixes #115

startLiveActivity was sending activityId as the bridge key, but StartVoltraOptions declares @Field activityName. so the value was silently dropped — activities always got a random UUID instead

Changes

• Renamed activityId to activityName in the TS bridge types and call sites so the key matches Swift.
• Fixed the unit test that was asserting the wrong key.

Test plan

• npm test — unit tests pass (including corrected activityName preserved test)
• npm run build — type checking