v2 Phase 4: add "generated" (output) tokens under the total on Session

The total is ~97% cache reads, which reads as implausibly large on its own.
Show the cache-inclusive total as the headline token number and the output
tokens ("what Claude actually generated", ~1.1M) as a small line beneath it —
impressive total, believable sub-number. Daemon sends a new `to` field; firmware
parses output_today and renders it. Re-spaced the Session layout for the 5th row.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

firmware/src/data.h

@@ -13,6 +13,7 @@ struct UsageData {
     // Today's Claude Code usage (Phase 4 — computed by the daemon from local
     // transcripts). Tokens can exceed 2^31 on a heavy day, so use 64-bit.
     long long tokens_today;     // total tokens today (input+output+cache)
+    long long output_today;     // output tokens today (what Claude generated)
     int       cost_cents_today; // equivalent API cost today, US cents
-    int       messages_today;   // assistant messages today
+    int       messages_today;   // assistant requests (API turns) today
 };