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/message.hpp

@@ -1569,8 +1569,8 @@ class PocsagTosendMessage : public Message {
     constexpr PocsagTosendMessage(
         uint16_t baud = 1200,
         uint8_t type = 2,
-        char function = 'D',
-        char phase = 'N',
+        char function = 'A',
+        char polarity = 'S', /* 'S' = Standard (CCIR Rec. 584), 'I' = Inverted */
         uint8_t msglen = 0,
         uint8_t msg[31] = {0},
         uint64_t addr = 0)
@@ -1578,15 +1578,15 @@ class PocsagTosendMessage : public Message {
           baud{baud},
           type{type},
           function{function},
-          phase{phase},
+          polarity{polarity},
           msglen{msglen},
           addr{addr} {
         memcpy(this->msg, msg, 31);
     }
     uint16_t baud = 1200;
     uint8_t type = 2;
-    char function = 'D';
-    char phase = 'N';
+    char function = 'A';
+    char polarity = 'S'; /* 'S' = Standard, 'I' = Inverted */
     uint8_t msglen = 0;
     uint8_t msg[31] = {0};
     uint64_t addr = 0;