Icon Request: circadian_rhythm

### Icon Request: circadian_rhythm

**Problem Statement**
Sleep tracking, wellness, and health apps are increasingly focused on circadian biology and chronobiology. Currently, Material Design has icons for sleep (`bedtime`, `nights_stay`, `bed`) and sun (`brightness`, `sunny`, `wb_sunny`), but none specifically represent the circadian rhythm — the body's natural 24-hour sleep-wake cycle that regulates health, energy, and sleep quality. A dedicated icon would help apps communicate this concept visually.

**Icon Description**
- **Basic Shape**: A circular or curved design with a half-sun/half-moon arc and a body or clock element
- **Key Features**:
- A curved arc showing the transition from sun to moon (or day to night)
- A human silhouette or body shape within/around it (representing the human biological rhythm)
- Alternative: A clock face with sun on one side and moon on the other
- Alternative: A body with "energy waves" or bio-rhythm indicators
- **Style**: Filled or Outlined
- **Scale**: Should be recognizable at 24dp to 48dp

**Concept Variations**
1. Sun-to-moon arc with body: Curved arc transitioning from sun to moon, with a human silhouette inside
2. Body with internal clock: Human silhouette with a clock/bio-clock element
3. Circular sun/moon cycle: Full circle with sun on one half, moon on the other
4. Person with circadian wave: Human silhouette with a wave pattern (like the circadian curve)

**References**
- Related icons in Material: `bedtime`, `nights_stay`, `sunny`, `wb_sunny`, `bed`
- Wellness apps: Sleep Cycle, Alarmy, RISE, Apple Health, Fitbit
- Scientific representations of the circadian cycle

**Justification**
- Sleep wellness is a multi-billion dollar industry
- Circadian biology is increasingly understood by the general public
- Currently no icon representing this holistic concept
- Health apps need this for sleep tracking and health monitoring

**Use Cases**
- Sleep tracking apps (Sleep Cycle, Pillow)
- Wellness/health apps (Apple Health, Samsung Health)
- Alarm clock apps with smart wake-up
- Bio-hacking/morning routine apps
- Health monitoring dashboards
- Fitness apps with sleep recovery tracking

**Search Keywords**
circadian rhythm, sleep cycle, body clock, biological clock, sleep-wake cycle, chronobiology, sleep health

**Similar Existing Icons**
- `bedtime` - moon + person sleeping
- `nights_stay` - moon
- `sunny` - sun
- `bed` - bed
- `alarm` - alarm clock

**Verification**
- [x] I checked https://fonts.google.com/icons and this specific icon does not exist
- [x] I searched for "circadian" and found no relevant icons
- [x] I understand I'm submitting a concept, not a finished design

**Note:** I understand that Google Fonts does not accept user submissions of finished icon designs (like SVG files) due to strict design guidelines, and that this repository is generated from upstream source files. I am submitting this as a concept for discussion, not a finished design.

Start by reviewing the related Material icons named in the issue and the upstream source files that generate this repository. Compare the proposed circadian concepts against Material Design guidelines and 24dp–48dp readability. Done means an agreed icon direction that fits the guidelines; no implementation file or test is identified here.

Written by the indexing model from the issue text.