v0.0.41: FC-P6-T2 — read receipts when messages are visible

- ChatLine gains sender_fp field for tracking who sent each message
- App gains read_receipts_sent HashSet to avoid duplicate receipts
- After each draw(), visible received messages get a Read receipt sent
- Only fires once per message_id, skips system/self messages
- Sender sees blue ✓✓ (existing display logic already handles Read)
- All ChatLine literals across 6 files updated with sender_fp field

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/Cargo.lock

@@ -2956,7 +2956,7 @@ dependencies = [
 
 [[package]]
 name = "warzone-client"
-version = "0.0.39"
+version = "0.0.40"
 dependencies = [
  "anyhow",
  "argon2",
@@ -2989,7 +2989,7 @@ dependencies = [
 
 [[package]]
 name = "warzone-mule"
-version = "0.0.39"
+version = "0.0.40"
 dependencies = [
  "anyhow",
  "clap",
@@ -2998,7 +2998,7 @@ dependencies = [
 
 [[package]]
 name = "warzone-protocol"
-version = "0.0.39"
+version = "0.0.40"
 dependencies = [
  "base64",
  "bincode",
@@ -3023,7 +3023,7 @@ dependencies = [
 
 [[package]]
 name = "warzone-server"
-version = "0.0.39"
+version = "0.0.40"
 dependencies = [
  "anyhow",
  "axum",
@@ -3054,7 +3054,7 @@ dependencies = [
 
 [[package]]
 name = "warzone-wasm"
-version = "0.0.39"
+version = "0.0.40"
 dependencies = [
  "base64",
  "bincode",