feat(app): Phase 2 — network HIL transport + source/demo UI + raw-HIL TX

[knaufinator]

App-side of the HIL network bridge (HIL_BRIDGE.md Phase 2; DECISIONS rounds 3 + 4). The app can now drive the ESP32 "mini" over the Voron bridge (UDP motion + line-JSON TCP control) alongside direct USB serial, and can stream pre-cueing RAW telemetry so the single on-device cue engine owns the feel for demo and live.

What's in it

Transport abstraction

• New app/src/transport.h: ITransport — a ~16-method superset interface (the HIL device card reads SerialPort-specific stats), kind() {Serial,Network}, moved ESP32Telemetry, and sendCobsDataRaw().
• SerialPort : public ITransport (all methods override). The six COBS decode counters move from public atomics → private + cobs*() accessors; the one reader in ui_panels.cpp updated.
• Entity::serial → shared_ptr<ITransport>. test_harness_panel's own dev-serial stays a concrete SerialPort (separate tool — not migrated).

New COBS raw channel

• cobs.h: COBS_CH_DATA_RAW = 0x07 (6×float32 LE, pre-cueing, app axis order surge=0/sway=1). Baked 0x06 (uint24, with swap) unchanged.

UdpTransport (app/src/udp_transport.{h,cpp})

• Same COBS frames as serial_port.cpp, emitted via winsock sendto() (one datagram = one frame), baked 0x06 or raw 0x07.
• Opens the bridge line-JSON TCP control port (default 8789), reusing the control_server.cpp winsock+cJSON pattern (no WebSocket dep). Decodes bridge status/telemetry/resp/log events → getLatestTelemetry()/drainLines(), so the existing app pipeline drives it unchanged.

Raw-HIL, capability-gated

• FINGERPRINT handler parses caps=raw / rawhil=1 → Entity::hil_cap_raw. When hil_cap_raw && hil_raw_mode, hilTxLoop TX's input_pct (pre-cueing, app order, no swap) as float32 on 0x07; else baked path unchanged. Old firmware omits the flag → baked. Network connect implies the raw path.

Connection + source/demo UI (ui_panels.cpp)

• Serial|Network selector + host / UDP / TCP fields; Network Connect builds UdpTransport + TCP control client and bypasses the serial FINGERPRINT handshake (bridge/ESP own identity + cueing). Serial path unchanged.
• OFF/DEMO/LIVE source selector + play + demo panel (list_files/mem/select_demo/upload_file[Burn]/delete) inside the HIL card, Network-only, driving the bridge TCP-JSON verbs. New fields persisted in settings.

.m6p raw export (change-list a)

• control_server.cpp export_sequence gains raw=1 → M6P2 header + 6×float32 LE pre-cueing samples (no swap); baked M6P1 export unchanged.

Build-verify (espressif cmake 3.30.2 / VS2022)

• Unit tests: 47/47 pass.
• SIL app (app/): configures, compiles, links clean (FetchContent glfw/imgui/implot/cJSON).
• No hardware run; not merged.

Open questions

See PR discussion / agent summary — notably network-path handshake semantics, caps=raw firmware token spelling, and Burn/upload being a bridge STUB until Phase-3 firmware.

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