FLEX RX: comprehensive decoder rewrite (#3131)

Baseband (proc_flex.cpp):
- Fix numeric vector field width (3-bit n+1 for types 3,4,7)
- Fix capcode range classification for long address components
- Add long address decode (Set 1-2, 1-3/1-4, 2-3)
- Add vector checksum validation (4-bit nibble sum)
- Add tone-only boundary detection via vector pre-scan
- Add idle phase detection (skip all-zeros/all-ones before BCH)
- Skip spurious TON for capcode 1 (BCH-corrected idle artifact)
- Add BIW parsing: SSID1/SSID2, DATE, TIME, TZ, SYSMSG, CHAN
- Add alpha fragment flags: frag, more_frag, seq, new, maildrop, sig
- Add secure message enc= field (alpha/binary/separate)
- Add numbered numeric flags: seq, new, fmt
- Add HEX/Binary header decode: block_bits, new, maildrop, rtl
- Add short instruction decode: temp group slot/target, sys events
- Add short message (SMSG) decode: tone/numeric/source/numbered
- Add group/temp-group/priority flags per address
- Add S2 C-pattern detection with ±1 symbol boundary correction
- Extract FIW roaming, repeat, traffic fields
- Replace snprintf with lightweight str_* helpers (no heap/_sbrk)
- Mark uncorrectable BCH words as ? instead of aborting phase
- ETX/NUL handling: trim trailing padding, show mid-message as ?

App (ui_flex_rx.cpp):
- Add status bar: cycle/frame, bitrate, polarity, time, timezone
- Add network info bar: LID, CZ, CC, roaming flag
- Pipe-delimited serial output for all message types
- BIW events to serial and status bar (not console)
- Human-readable console: +GRP for temp group, G/TG/P flags
- USB serial via UsbSerialAsyncmsg

Packet (flex_defs.hpp):
- uint64_t capcode (long address support)
- 256-byte message buffer
- Fragment flags, BIW raw values, address type, group/priority

Known limitation: phase label unreliable on multi-phase modes
(3200/2FSK, 6400/4FSK). Data always decodes correctly.

firmware/application/external/flex_rx/ui_flex_rx.hpp

@@ -26,10 +26,17 @@ class FlexAppView : public View {
     NavigationView& nav_;
 
     // Saved settings
-    rf::Frequency frequency_value{931740000};  // Default FLEX frequency
+    rf::Frequency frequency_value{931740000};
 
     RxRadioState radio_state_{};
 
+    // Status bar state (updated from BIW packets)
+    char status_time_[12]{};  // "HH:MM:SS"
+    char status_tz_[12]{};    // "UTC+N"
+    uint16_t status_lid_{0};
+    uint16_t status_cz_{0};
+    uint16_t status_cc_{0};
+
     // Message storage for console redraw
     static constexpr size_t MAX_MESSAGES = 20;
     std::vector<std::string> messages{};
@@ -54,9 +61,17 @@ class FlexAppView : public View {
     RSSI rssi{
         {UI_POS_X(21), 0, UI_POS_WIDTH(9), 4}};
 
-    // Message display area (below controls, account for status bar)
+    // Status rows (rows 1-2)
+    Text text_status1{
+        {0, 1 * 16, screen_width, 16},
+        ""};
+    Text text_status2{
+        {0, 2 * 16, screen_width, 16},
+        ""};
+
+    // Message display area (below status rows)
     Console console{
-        {0, 1 * 16, screen_width, screen_height - 2 * 16}};
+        {0, 3 * 16, screen_width, screen_height - 4 * 16}};
 
     // Persistent settings manager
     app_settings::SettingsManager settings_{