feat: initial Xiao RP2040 mouse jiggler firmware

Embassy-based no_std firmware for the Seeed Studio Xiao RP2040 that
masquerades as a Dell MS116 USB HID Boot Mouse. Each cycle picks a
random axis from the RP2040 ROSC RANDOMBIT register, nudges +1 px,
dwells 25 ms, nudges -1 px, then sleeps 4.5 minutes. After 8 hours
elapsed from boot or RESET press the device idles silently (watchdog
still fed) until the user taps RESET (R) again, aligning a single
press with one workday.

Tooling:
- mise.toml pins rust 1.95.0 with explicit components and the
  thumbv6m-none-eabi target, plus cargo-binutils / uf2conv helpers.
- justfile shell is set to "mise exec -- sh -eu -c" so every recipe
  uses the pinned toolchain without any shell activation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name    = "jiggly"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+embassy-executor = { version = "0.10.0", features = ["platform-cortex-m", "executor-thread"] }
+embassy-time     = { version = "0.5.1" }
+embassy-rp       = { version = "0.10.0", features = ["rp2040", "time-driver", "critical-section-impl", "unstable-pac"] }
+embassy-usb      = "0.6.0"
+usbd-hid         = "0.10.0"
+
+cortex-m        = { version = "0.7.6", features = ["inline-asm"] }
+cortex-m-rt     = "0.7.5"
+panic-reset     = "0.1"
+static_cell     = "2.1"
+portable-atomic = { version = "1.13", features = ["critical-section"] }
+
+[profile.release]
+lto             = true
+opt-level       = "s"
+codegen-units   = 1
+debug           = 2
+overflow-checks = false