Boundary mode: performance optimizations + boundary filter

Performance optimizations:
- Move TLSF allocator pool to PSRAM (frees ~170KB internal SRAM)
- Raise TCP_IF_MAX_CLIENTS from 4 to 8 in BOUNDARY_MODE
- Raise path_table_maxsize from 48 to 128, persist from 16 to 32
- Add -DNDEBUG to boundary build: compiles out TRACE/DEBUG macros
- Log level defaults to LOG_VERBOSE when NDEBUG defined
- Serial baud 115200 -> 921600 in BOUNDARY_MODE (reduces CPU blocking)

Previous changes included in this commit:
- Comprehensive boundary filter with transitive whitelisting (7 checks)
- destination_table erase+insert fix (std::map::insert no-overwrite bug)
- Backbone-to-backbone routing guard in next-hop forwarding
- KISS serial output disabled for boundary mode
- flash.py updates for boundary mode support

RNode_Firmware.ino

@@ -647,13 +647,12 @@ void setup() {
       // ── Boundary Mode: Load config and optionally set up WiFi + TCP ──
       HEAD("Boundary Mode: Initializing...", RNS::LOG_TRACE);
 
-      // Reduce table sizes to conserve heap on ESP32.
-      // Default 100 entries for each table fragments heap to critical levels.
-      // 48 entries gives enough room for local paths plus some backbone paths.
+      // With TLSF pool moved to PSRAM we have plenty of room.
+      // 128 path entries supports ~15-20 devices comfortably.
       // cull_path_table() is patched to evict backbone paths first, preserving
       // local (LoRa / local-TCP) paths needed for inbound message delivery.
-      RNS::Transport::path_table_maxsize(48);
-      RNS::Transport::path_table_maxpersist(16);
+      RNS::Transport::path_table_maxsize(128);
+      RNS::Transport::path_table_maxpersist(32);
       boundary_load_config();
 
       // Start WiFi if enabled