chore(firmware): scaffold Spike 1 Blink crate

Generated from esp-rs/esp-idf-template for the ESP32-S3 std target.
src/main.rs toggles GPIO 2 every 500 ms and logs `blink N` over USB-
serial — the minimum bring-up surface called out in
docs/v0.1-mvp-technical.md (Spike 1: confirm toolchain, flash, and basic
GPIO). edition=2024 with rust-version=1.85.

No editor/render/git/usb/fs modules yet; those land per the spike
methodology when later spikes need them.

firmware/Cargo.toml

@@ -0,0 +1,32 @@
+[package]
+name = "firmware"
+version = "0.1.0"
+authors = ["Julien Calixte <julien.calixte@theodo.com>"]
+edition = "2024"
+resolver = "2"
+rust-version = "1.85"
+
+[[bin]]
+name = "firmware"
+harness = false # do not use the built-in cargo test harness -> resolve rust-analyzer errors
+
+[profile.release]
+opt-level = "s"
+
+[profile.dev]
+debug = true    # Symbols are nice, and they don't increase the size on Flash
+opt-level = "z"
+[patch.crates-io]
+esp-idf-sys = { git = "https://github.com/esp-rs/esp-idf-sys.git" }
+esp-idf-hal = { git = "https://github.com/esp-rs/esp-idf-hal.git" }
+esp-idf-svc = { git = "https://github.com/esp-rs/esp-idf-svc.git" }
+
+[dependencies]
+anyhow = "1"
+log = "0.4"
+esp-idf-svc = { version = "0.52.1", features = ["critical-section", "embassy-time-driver", "embassy-sync"] }
+# Remove `generic-queue-8` if you plan to use `embassy-time` WITH `embassy-executor`
+embassy-time = { version = "0.5", features = ["generic-queue-8"] }
+
+[build-dependencies]
+embuild = "0.33"