spec: add psychrometric-basic specification

plots/psychrometric-basic/specification.md

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+# psychrometric-basic: Psychrometric Chart for HVAC
+
+## Description
+
+A psychrometric chart plots dry-bulb temperature against humidity ratio, overlaid with curves for relative humidity, wet-bulb temperature, enthalpy, and specific volume. It is the fundamental tool for HVAC system design and air conditioning process analysis. The chart reveals the thermodynamic properties of moist air at a glance, enabling engineers to trace heating, cooling, humidification, and dehumidification processes as paths on the diagram.
+
+## Applications
+
+- HVAC engineering: designing and analyzing air conditioning systems by tracing process paths (heating, cooling, mixing) on the chart
+- Building science: evaluating indoor thermal comfort zones and identifying condensation risks
+- Industrial process engineering: optimizing drying operations and clean room environmental control
+
+## Data
+
+- `dry_bulb_temp` (float) - Dry-bulb air temperature in degrees Celsius, x-axis primary variable
+- `humidity_ratio` (float) - Mass of water vapor per mass of dry air in g/kg, y-axis primary variable
+- `relative_humidity` (float[]) - Constant relative humidity curves from 10% to 100% in 10% increments
+- `wet_bulb_temp` (float[]) - Diagonal lines of constant wet-bulb temperature
+- `enthalpy` (float[]) - Oblique lines of constant enthalpy in kJ/kg
+- `specific_volume` (float[]) - Lines of constant specific volume in m3/kg
+- Size: derived from psychrometric equations over a dry-bulb range of -10 to 50 degrees Celsius
+- Example: standard atmosphere (101.325 kPa) psychrometric properties computed from ASHRAE formulas
+
+## Notes
+
+- The saturation curve (100% RH) forms the upper boundary of the chart and should be visually prominent
+- Relative humidity curves (10%-100%) should be drawn as smooth curves between the saturation line and x-axis
+- Wet-bulb and enthalpy lines run diagonally from upper-left to lower-right
+- Specific volume lines run at a slightly different diagonal angle
+- Include at least one example HVAC process path (e.g., cooling and dehumidification) shown as an arrow or highlighted line segment between two state points
+- A comfort zone region (approximately 20-26 C, 30-60% RH) should be highlighted as a shaded rectangle or polygon
+- All property lines should be labeled directly on the chart, not just in a legend
+- Use standard sea-level atmospheric pressure (101.325 kPa) for calculations

plots/psychrometric-basic/specification.yaml

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+# Specification-level metadata for psychrometric-basic
+# Auto-synced to PostgreSQL on push to main
+
+spec_id: psychrometric-basic
+title: Psychrometric Chart for HVAC
+
+# Specification tracking
+created: "2026-03-06T19:54:00Z"
+updated: null
+issue: 4583
+suggested: MarkusNeusinger
+
+# Classification tags (applies to all library implementations)
+# See docs/reference/tagging-system.md for detailed guidelines
+tags:
+  plot_type:
+    - line
+    - contour
+  data_type:
+    - numeric
+    - continuous
+  domain:
+    - engineering
+    - energy
+  features:
+    - advanced
+    - annotated
+    - multi