fix: no flash writes while typing, and a clock that survives a power loss

Contacts and paths are saved a while after the change and never while the
user is active, so a send no longer stutters on the 53 KB contact rewrite
(a path that came back unchanged isn't written at all). The clock is saved
every 30 minutes and restored no earlier than the firmware's build day.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/MyMesh.h

@@ -428,7 +428,11 @@ public:
   // this before rebooting; UITask::shutdown() (low-battery auto-shutdown,
   // long-press power-off) needs the same flush or a whole session's worth
   // of learned contacts can be lost.
-  void flushDirtyContacts() { if (dirty_contacts_expiry) { saveContacts(); dirty_contacts_expiry = 0; } }
+  void flushDirtyContacts() {
+    if (dirty_contacts_expiry || dirty_paths_expiry) { saveContacts(); dirty_contacts_expiry = dirty_paths_expiry = 0; }
+  }
+  // A key press / touch: the lazy contacts write waits until the user pauses.
+  void noteUserInput() { _last_input_ms = millis(); }
   DataStore* getDataStore() const { return _store; }
   void applyApc();   // (re)initialise Adaptive Power Control from prefs
   // Adaptive Power Control is suppressed while repeating: a repeater wants full,
@@ -649,6 +653,10 @@ private:
   uint32_t sign_data_len;
   uint32_t sign_data_cap;   // what the malloc got: at most MAX_SIGN_DATA_LEN
   unsigned long dirty_contacts_expiry;
+  unsigned long dirty_paths_expiry = 0;   // only paths changed: written later (not pending work)
+  unsigned long _last_input_ms = 0;
+  unsigned long _last_rtc_save_ms = 0;
+  bool _path_same = false;                // onContactPathRecv(): the path heard is the one held
   unsigned long _bot_last_ch_reply_ms;
   unsigned long _bot_last_room_reply_ms;
   unsigned long _next_auto_advert_ms;