feat: Phase 1 firmware — time-multiplexed tri-protocol RX scanner

First Phase 1 increment toward the single-device 3-in-1: one Heltec V3
(ESP32-S3 + single SX1262) rotating the radio through the Meshtastic /
MeshCore / Reticulum PHY presets, logging every raw packet it demodulates
per dwell window. No framing/crypto/bridge yet — proves the RX loop first.

Validated on hardware: radio.begin() clean, all three presets cycle, and
the Meshtastic window received live broadcast packets (-36..-41 dBm). The
single-radio time-multiplex premise (ARCHITECTURE.md §2) holds.

MeshCore sync word and Reticulum PHY are flagged placeholders in CONFIGS[].
Deps pinned (espressif32 7.0.1, RadioLib 7.7.1). Adds venv/pycache/storage
to .gitignore.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -3,3 +3,12 @@
 build/
 .pio/
 .vscode/
+
+# Python (host-bridge)
+venv/
+__pycache__/
+*.pyc
+
+# Reticulum/LXMF runtime storage
+rns-storage/
+rns-store/