fix: reduce event expiration to 20s and fix foreground service crash

- Change EXPIRATION_SECONDS from 300 to 20 for all call signaling
  events (offer, answer, ICE, hangup, reject, renegotiate)
- Change MAX_EVENT_AGE_SECONDS from 30 to 20 to match
- Update NIP-AC doc accordingly
- Fix SecurityException crash on SDK 36: phoneCall foreground service
  type requires MANAGE_OWN_CALLS permission. Switch to microphone
  type which only needs RECORD_AUDIO (already granted).

https://claude.ai/code/session_017hZm7yu7CzmcQgZGSaqSXS

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/NIP-AC.md

@@ -215,7 +215,7 @@ This NIP does not mandate specific STUN or TURN servers. Clients SHOULD:
 ## Implementation Notes
 
 - The `call-id` tag MUST be a UUID that is unique per call session. All signaling events for the same call share the same `call-id`.
-- Events SHOULD have short expiration times (~5 minutes) since signaling data is ephemeral and has no long-term value.
+- Events SHOULD have short expiration times (~20 seconds) since signaling data is ephemeral and has no long-term value.
 - Clients SHOULD implement a ringing timeout (e.g., 60 seconds). If no answer is received, the call transitions to a "timed out" state.
 - Clients SHOULD use a foreground service or equivalent mechanism to keep calls active when the app is backgrounded.
 - The WebRTC `PeerConnection` SHOULD use Unified Plan SDP semantics.

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/events/CallAnswerEvent.kt

@@ -48,7 +48,7 @@ class CallAnswerEvent(
     companion object {
         const val KIND = 25051
         const val ALT_DESCRIPTION = "WebRTC call answer"
-        const val EXPIRATION_SECONDS = 300L
+        const val EXPIRATION_SECONDS = 20L
 
         fun build(
             sdpAnswer: String,

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/events/CallHangupEvent.kt

@@ -48,7 +48,7 @@ class CallHangupEvent(
     companion object {
         const val KIND = 25053
         const val ALT_DESCRIPTION = "WebRTC call hangup"
-        const val EXPIRATION_SECONDS = 300L
+        const val EXPIRATION_SECONDS = 20L
 
         fun build(
             peerPubKey: HexKey,

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/events/CallIceCandidateEvent.kt

@@ -48,7 +48,7 @@ class CallIceCandidateEvent(
     companion object {
         const val KIND = 25052
         const val ALT_DESCRIPTION = "WebRTC ICE candidate"
-        const val EXPIRATION_SECONDS = 300L
+        const val EXPIRATION_SECONDS = 20L
 
         fun build(
             candidateJson: String,

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/events/CallOfferEvent.kt

@@ -53,7 +53,7 @@ class CallOfferEvent(
     companion object {
         const val KIND = 25050
         const val ALT_DESCRIPTION = "WebRTC call offer"
-        const val EXPIRATION_SECONDS = 300L // 5 minutes
+        const val EXPIRATION_SECONDS = 20L
 
         fun build(
             sdpOffer: String,

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/events/CallRejectEvent.kt

@@ -48,7 +48,7 @@ class CallRejectEvent(
     companion object {
         const val KIND = 25054
         const val ALT_DESCRIPTION = "WebRTC call rejection"
-        const val EXPIRATION_SECONDS = 300L
+        const val EXPIRATION_SECONDS = 20L
 
         fun build(
             callerPubKey: HexKey,

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/events/CallRenegotiateEvent.kt

@@ -48,7 +48,7 @@ class CallRenegotiateEvent(
     companion object {
         const val KIND = 25055
         const val ALT_DESCRIPTION = "WebRTC call renegotiation"
-        const val EXPIRATION_SECONDS = 300L
+        const val EXPIRATION_SECONDS = 20L
 
         fun build(
             sdpOffer: String,