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

TcpInterface.h

@@ -23,7 +23,11 @@
 
 // ─── TCP Interface Configuration ─────────────────────────────────────────────
 #define TCP_IF_DEFAULT_PORT      4242
+#ifdef BOUNDARY_MODE
+#define TCP_IF_MAX_CLIENTS       8
+#else
 #define TCP_IF_MAX_CLIENTS       4
+#endif
 #define TCP_IF_HW_MTU            1064
 #define TCP_IF_CONNECT_TIMEOUT   6000    // ms
 #define TCP_IF_WRITE_TIMEOUT     2000    // ms — short to avoid WDT