Initial public release of WII5 Buoy firmware

Firmware for an autonomous wave-measurement buoy (ATmega2560-based
WII5 v2 board). Reads wave motion from a Sparton AHRS-M1/M2 IMU,
samples GPS and battery state, and reports back over Iridium SBD
satellite telemetry. Originally developed 2012-2024.

This is the first public release. Code, documentation, and field-tested
operating modes (Capture, Sleep, Position, ManualTest, SelfTest,
LowBattery) are licensed under Apache 2.0 — see LICENSE and NOTICE.

See README.md for an overview and build instructions, CONTRIBUTING.md
for how to contribute, and DEPLOYMENTS.md for the field-deployment log.

DEPLOYMENTS.md

@@ -0,0 +1,37 @@
+# Field Deployments
+
+A running log of notable field deployments of the WII5 buoy firmware.
+This file is for crediting partners, recording lessons learned, and
+documenting which firmware version went out the door for each campaign.
+
+Add a new section per deployment. Keep them short — link out to papers,
+mission reports, or partner sites for the full story.
+
+---
+
+## Template
+
+### YYYY — Deployment name
+
+- **Partner / institution:** ...
+- **Location:** ... (broad region; do not record exact buoy coordinates here)
+- **Firmware version:** `vX.Y.Z` (commit `<short-sha>`)
+- **Hardware:** WII5 v2 board, Sparton AHRS-M*, Iridium 9602 / 9603, etc.
+- **Mode profile:** Capture / Position / Sleep schedule used in the field
+- **Notes:** field issues observed, fixes that came out of the campaign,
+  links to publications.
+
+---
+
+<!--
+Add real deployments below. Suggested first entry:
+
+### 2024 — KOPRI deployment
+
+- **Partner:** Korea Polar Research Institute (KOPRI)
+- **Firmware version:** v5.5.x
+- **Hardware:** WII5 v2 board with Sparton AHRS-M2, Iridium 9603
+- **Notes:** ...
+
+(Confirm with KOPRI before listing publicly.)
+-->