fix(qemu): resolve 23 bugs from deep code review

CRITICAL:
- inject_fault.py: make nvs_corrupt write actual bytes via --flash arg;
  heap_exhaust and corrupt_frame now pause VM with honest WARNING about
  GDB stub requirement for real memory writes
- firmware-qemu.yml: remove github.run_id from cache key (was causing
  100% cache miss rate, rebuilding QEMU every run)
- mock_csi.c: change scenario_elapsed_ms() to int64_t (uint32 wrapped
  at ~49 days)

HIGH:
- qemu-mesh-test.sh: pass --results flag to validate_mesh_test.py
  (was passing positional arg to named-only parameter)
- test/Makefile: separate corpus directories per fuzz target
  (corpus_serialize/, corpus_edge/, corpus_nvs/)
- qemu-snapshot-test.sh: replace log truncation with tail-based
  extraction (truncation created sparse file while QEMU held fd)

MEDIUM:
- mock_csi.c: reset s_mac_filter_initialized in mock_csi_init()
- mock_csi.c: fix LFSR polynomial comment (32,31,29,1 not 32,22,2,1)
- sdkconfig.coverage: add FreeRTOS timer stack 4096 and WDT tuning
- firmware-qemu.yml: replace continue-on-error with FUZZER_CRASH env
- qemu-chaos-test.sh: rename heap_pressure to heap_exhaust for consistency
- validate_qemu_output.py: fix docstring "14 checks" -> "16 checks"
- generate_nvs_matrix.py: deduplicate temp file cleanup paths

LOW:
- mock_csi.c: remove M_PI float suffix, fix overflow burst flag
- qemu-snapshot-test.sh: fix now_ms() for macOS date +%s%N
- ADR-061: fix scenario 8 RSSI range to -90...-10 dBm
- launch.json: remove contradictory compound debug config

Co-Authored-By: claude-flow <ruv@ruv.net>

docs/adr/ADR-061-qemu-esp32s3-firmware-testing.md

@@ -237,7 +237,7 @@ This model exercises:
 | 5 | Channel sweep | 5s | Frames on channels 1, 6, 11 in sequence |
 | 6 | MAC filter test | 5s | Frames with wrong MAC are dropped (counter check) |
 | 7 | Ring buffer overflow | 3s | 1000 frames in 100ms burst, graceful drop |
-| 8 | Boundary RSSI | 5s | RSSI sweeps -127 to 0, no crash |
+| 8 | Boundary RSSI | 5s | RSSI sweeps -90 to -10 dBm, no crash |
 | 9 | Zero-length frame | 2s | `iq_len=0` frames, serialize returns 0 |
 
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