Implement versioned NVS key migration on ESP32-S3 firmware so
OTA-updated firmware gracefully handles NVS written by older versions.
- Add nvs_migration.c/h with migration framework
- On boot, read schema_ver from NVS; initialize to 1 if missing
- Run migrations sequentially if schema_ver < COMPILED_NVS_VERSION
- Each migration commits after each write for durability
- Log all migration steps to UART for debugging
- Example migration v1→v2: rename 'ms_ip' to 'mothership_ip',
add 'ntp_server' with default 'pool.ntp.org'
- Migration failure leaves NVS in consistent state
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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