[bseverns]

Motivation

• Make it easier for newcomers and instructors to find per-sensor wiring, RC recipes, calibration rituals, and expected gesture behavior.
• Surface the intent and normalization behavior of each sensor read path so classroom narration matches the implementation.
• Keep the Sensor abstraction teachable and reduce onboarding time during live demos.

Description

• Add a short field-notes index at docs/Sensors/README.md that links to each per-sensor page and gives a quick teaching flow.
• Cross-link the index from docs/SensingSurvey.md and the top-level README.md so the notes show up in the onboarding paths.
• Clarify inline comments in firmware sensor implementations to explicitly call out normalization behavior (and small wording tweaks) in firmware/src/time_of_flight_sensor.cpp, firmware/src/piezo_sensor.cpp, firmware/src/pir_sensor.cpp, firmware/src/electret_mic_sensor.cpp, and firmware/src/i2s_mic_sensor.cpp.
• Changes are documentation and comment updates; no sensor logic or public API surface was changed.

Testing

• No automated tests were run for this change because it is documentation and comment updates only.
• No firmware/device builds were executed as part of this PR.
• Docs-only changes were added to the repo and committed; local docs render was not validated by CI in this rollout.
• If desired, run pio test -d firmware -e native and CI build targets to smoke-check firmware builds after these edits.

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Codex Task