refactor(companion): dedup age formatting + reply-prefix parsing; drop dead code

Consolidation pass over the message/nearby UI, no functional change beyond
one intentional display tweak:

- Age tags: NearbyScreen::fmtAge, the nearby list's inline column, and
  QuickMsgScreen::fmtMsgAge each reimplemented the same s/m/h bucket ladder
  on top of geo::fmtAgeShort. All now delegate to it (fmtMsgAge removed).
  Visible effect: ages over 24h render as "Nd" instead of capped hours,
  matching the Locator target picker which already used fmtAgeShort.
- Reply prefix: the "@[nick] " parse was duplicated in skipReplyPrefix() and
  FullscreenMsgView::render(). Extracted to one msgReplyBody() helper (body,
  plus optional addressee nick) — one place to handle its edge cases.
- LiveTrack: the expiry predicate was duplicated in expire()/isActive();
  extracted to a private expired() helper.
- Removed a dead M_PI define (and unused <math.h>) in NearbyScreen.h, and a
  comment pointing at a CODE_REVIEW.md that doesn't exist.

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

examples/companion_radio/ui-new/NearbyScreen.h

@@ -1,12 +1,7 @@
 #pragma once
-#include <math.h>
 #include "../GeoUtils.h"
 #include "NavView.h"
 
-#ifndef M_PI
-  #define M_PI 3.14159265358979323846
-#endif
-
 // ── Nearby Nodes ──────────────────────────────────────────────────────────────
 // One list / detail / action-menu interaction path over two sources:
 //   SRC_STORED — contacts known to the mesh (distance / bearing / last-heard)
@@ -111,14 +106,13 @@ class NearbyScreen : public UIScreen {
 
   bool useImperial() const { return _task && _task->useImperial(); }
 
+  // Full "X ago" form for the detail view, built on the shared short-age tag
+  // so there's one bucket ladder (see geo::fmtAgeShort).
   static void fmtAge(char* buf, int n, uint32_t lastmod) {
-    uint32_t now = rtc_clock.getCurrentTime();
-    if (now < lastmod || lastmod == 0) { snprintf(buf, n, "unknown"); return; }
-    uint32_t age = now - lastmod;
-    if      (age < 60)     snprintf(buf, n, "%us ago",  age);
-    else if (age < 3600)   snprintf(buf, n, "%um ago",  age / 60);
-    else if (age < 86400)  snprintf(buf, n, "%uh ago",  age / 3600);
-    else                   snprintf(buf, n, ">1d ago");
+    char s[8];
+    geo::fmtAgeShort(s, sizeof(s), rtc_clock.getCurrentTime(), lastmod);
+    if (!s[0]) { snprintf(buf, n, "unknown"); return; }
+    snprintf(buf, n, "%s ago", s);
   }
 
   static const char* typeName(uint8_t t) {
@@ -715,14 +709,8 @@ public:
         if (_source == SRC_SCAN) {
           snprintf(right, sizeof(right), "%d", (int)e.rssi);
         } else if (_sort == SORT_TIME) {
-          uint32_t now = rtc_clock.getCurrentTime();
-          if (e.lastmod == 0 || now < e.lastmod)  snprintf(right, sizeof(right), "?");
-          else {
-            uint32_t age = now - e.lastmod;
-            if      (age < 60)   snprintf(right, sizeof(right), "%us", age);
-            else if (age < 3600) snprintf(right, sizeof(right), "%um", age / 60);
-            else                 snprintf(right, sizeof(right), "%uh", age / 3600);
-          }
+          geo::fmtAgeShort(right, sizeof(right), rtc_clock.getCurrentTime(), e.lastmod);
+          if (!right[0]) snprintf(right, sizeof(right), "?");   // unknown / RTC not synced
         } else {
           if (e.dist_km >= 0.0f) geo::fmtDist(right, sizeof(right), e.dist_km, useImperial());
           else                   strncpy(right, "?GPS", sizeof(right));