M1 step 3: Log writing and Storage Clean-up

- lib/storage_model (host-tested): FAT-safe names, daily Log paths,
  dates from Log/Capture file names, CleanupPlan by category and age,
  byte formatting
- StorageService does all card I/O on its task: queued Log lines are
  written in batches each second (dropped while Logs are paused),
  plus file listing and deletion jobs
- Settings > Storage moves into StoragePage: usage, Clean up
  (category, age with size preview, confirmation), Erase SD card
- Clock: local date for Log names
- Serial: log <text>, sd list

Verified on the device: lines land in /irc/dev/#test/2026-10-02.log
with folders created as needed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/services/clock_service.h

@@ -23,6 +23,11 @@ class ClockService : public Service {
     bool set(int64_t utcSeconds, TimeSource source) { return model_.set(utcSeconds, source, millis()); }
     const ClockModel& model() const { return model_; }
 
+    // Local "YYYY-MM-DD" once set; otherwise empty (Logs then go to undated files).
+    std::string localDate() const { return model_.isSet() ? ClockModel::formatLocalDate(model_.utcNow(millis())) : ""; }
+    // Days since 1970-01-01 (UTC), or -1 if the clock isn't set.
+    int today() const { return model_.isSet() ? static_cast<int>(model_.utcNow(millis()) / 86400) : -1; }
+
     // "14:05" once set; otherwise "--:--".
     std::string displayTime() const {
         return model_.isSet() ? ClockModel::formatLocalTime(model_.utcNow(millis())) : "--:--";