POCSAG: decoder fixes, serial output, TX polarity cleanup (#3130)

RX: fix address/batch-boundary handling, add numeric continuation,
add heuristic type detection toggle, pass inverted polarity flag,
stream decoded messages over USB serial.

TX: rename phase to polarity (Standard/Inverted), fix function
validation (&&→||), fix serial shell payload read (offset tracking,
31-byte cap, preserve msglen).

Decoder: remove color escapes from output (plain text for all
consumers), guard count_alpha_fill against empty string, keep
numeric_len across continuation batches.

Serial format: POCSAG <baud> <addr> <func> <pol> <type> "<msg>" hex:<hex>
Quote escaping for embedded " and \\ in alpha messages.

firmware/common/pocsag_packet.hpp

@@ -35,8 +35,7 @@ enum BitRate : uint32_t {
     UNKNOWN,
     FSK512 = 512,
     FSK1200 = 1200,
-    FSK2400 = 2400,
-    FSK3200 = 3200
+    FSK2400 = 2400
 };
 
 enum PacketFlag : uint32_t {
@@ -88,15 +87,25 @@ class POCSAGPacket {
         return flag_;
     }
 
+    void set_inverted(bool inverted) {
+        inverted_ = inverted;
+    }
+
+    bool inverted() const {
+        return inverted_;
+    }
+
     void clear() {
         codewords.fill(0);
         bitrate_ = 0u;
         flag_ = NORMAL;
+        inverted_ = false;
     }
 
    private:
     uint16_t bitrate_{0};
     PacketFlag flag_{NORMAL};
+    bool inverted_{false};
     batch_t codewords{};
     Timestamp timestamp_{};
 };