chore(firmware): mark TODOs for the dev-only 60s polling cap

Three cross-referenced markers — config.h, operation.h, and FW-10 in the
test file — calling out that the FETCH_INTERVAL_MS cap is intentionally
holding the polling rate at 1 minute for dev iteration. Once the firmware
is stable and we want the device to honor the app's per-frame
rotationIntervalMinutes / wakeHour settings, the cap in operation.h
becomes a sanity-clamp (e.g., 30 s ≤ sleep ≤ 25 h) and the no-header
fallback splits into its own constant.

Behavior unchanged — comments only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/operation.h

@@ -131,6 +131,15 @@ void normal_operation_impl(const String& mac, HTTP& http, const String& url, Pre
     http.collectHeaders(collectHeaders, 3);
     int code = http.GET();
 
+    // TODO(post-dev): trust the server's X-Interval-Ms instead of capping
+    // it at FETCH_INTERVAL_MS. The cap is here so the dev unit polls
+    // every minute regardless of what the app's rotationIntervalMinutes /
+    // wakeHour settings say — fast iteration. Once the firmware is stable
+    // and we want real battery life on V2, the line below should become
+    // simply `sleepMs = v;` plus a sanity clamp (e.g. min 30 s, max 25 h).
+    // Tests FW-09 and FW-10 in test_normal_operation/test_main.cpp lock
+    // the current behavior — update them when removing the cap. See the
+    // matching note in config.h on FETCH_INTERVAL_MS.
     uint64_t sleepMs = FETCH_INTERVAL_MS;
     String intervalHdr = http.header("X-Interval-Ms");
     if (intervalHdr.length() > 0) {