feat: opt-in Summon EU Unlock (0x3FD mux1 bit47) for HW3/HW4

[hypery11]

Adds an opt-in Summon EU Unlock toggle (default OFF) that clears the EU summon restriction bit and sets the summon-enable bit on 0x3FD (DAS_autopilotControl) mux 1, on both HW3 and HW4.

Background

The bits are the two documented in the ev-open-can-tools summon-eu-unlock.json plugin: 0x3FD mux 1, clear bit 19 (EU restriction), set bit 47 (summon enable). HW4 already set both as part of the AP-control injection; HW3 cleared bit 19 but never set bit 47, so this closes that gap and exposes it as an explicit, persisted, opt-in control. Refs #111, #139.

Changes

• fsd_state.h: new bool summon_unlock (default OFF).
• Flipper + ESP32 0x3FD handlers: set bit 47 under the flag. ESP32 mux-1 gate widened to (nag_killer || summon_unlock), with the nag bits kept inside if(nag_killer) so nag output is byte-for-byte identical when summon is off.
• prefs.cpp: NVS persistence (summon).
• web_dashboard.cpp: "Summon EU Unlock" toggle in Controls.
• test_fsd_core.c: test_summon_unlock (HW3/HW4 × on/off). 467 host tests pass.

Known limitations

• On the Flipper core, HW4 mux-1 sets bit 47 unconditionally (pre-existing, left untouched to avoid regressing nag behaviour), so the toggle only changes the HW3 frame there; ESP32 gates both. Reconciling this divergence is a follow-up.
• Flipper on-device menu item not added yet (ESP32 dashboard only).
• Not yet validated on a car — off by default; needs an on-car confirmation before it's recommended.