spec: add indicator-macd specification (#3186)

## New Specification: `indicator-macd`

Related to #3181

---

### specification.md

# indicator-macd: MACD Technical Indicator Chart

## Description

A MACD (Moving Average Convergence Divergence) chart displaying three
components: the MACD line, signal line, and histogram. The MACD line
represents the difference between 12-day and 26-day exponential moving
averages, while the signal line is a 9-day EMA of the MACD. The
histogram visualizes the difference between these two lines. This is an
essential momentum oscillator for technical analysis, helping traders
identify trend direction, momentum strength, and potential buy/sell
signals through line crossovers.

## Applications

- Analyzing stock price momentum to identify trend reversals and
entry/exit points
- Generating trading signals for cryptocurrency markets based on
MACD/signal line crossovers
- Confirming trend strength by observing histogram expansion or
contraction

## Data

- `date` (datetime) - Trading date or timestamp for each period
- `macd` (numeric) - MACD line value (12-day EMA minus 26-day EMA)
- `signal` (numeric) - Signal line value (9-day EMA of MACD)
- `histogram` (numeric) - Difference between MACD and signal line
- Size: 60-200 periods for meaningful pattern recognition
- Example: Daily MACD values calculated from stock closing prices over
120 trading days

## Notes

- Display histogram as bars with green (positive) and red (negative)
colors
- Include a zero reference line to highlight crossover signals
- MACD and signal lines should use distinct colors (e.g., blue and
orange)
- Standard parameters are 12, 26, 9 but should be noted in the chart
- Typically shown as a separate panel below a price chart, but can stand
alone

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plots/indicator-macd/specification.md

@@ -0,0 +1,28 @@
+# indicator-macd: MACD Technical Indicator Chart
+
+## Description
+
+A MACD (Moving Average Convergence Divergence) chart displaying three components: the MACD line, signal line, and histogram. The MACD line represents the difference between 12-day and 26-day exponential moving averages, while the signal line is a 9-day EMA of the MACD. The histogram visualizes the difference between these two lines. This is an essential momentum oscillator for technical analysis, helping traders identify trend direction, momentum strength, and potential buy/sell signals through line crossovers.
+
+## Applications
+
+- Analyzing stock price momentum to identify trend reversals and entry/exit points
+- Generating trading signals for cryptocurrency markets based on MACD/signal line crossovers
+- Confirming trend strength by observing histogram expansion or contraction
+
+## Data
+
+- `date` (datetime) - Trading date or timestamp for each period
+- `macd` (numeric) - MACD line value (12-day EMA minus 26-day EMA)
+- `signal` (numeric) - Signal line value (9-day EMA of MACD)
+- `histogram` (numeric) - Difference between MACD and signal line
+- Size: 60-200 periods for meaningful pattern recognition
+- Example: Daily MACD values calculated from stock closing prices over 120 trading days
+
+## Notes
+
+- Display histogram as bars with green (positive) and red (negative) colors
+- Include a zero reference line to highlight crossover signals
+- MACD and signal lines should use distinct colors (e.g., blue and orange)
+- Standard parameters are 12, 26, 9 but should be noted in the chart
+- Typically shown as a separate panel below a price chart, but can stand alone

plots/indicator-macd/specification.yaml

@@ -0,0 +1,30 @@
+# Specification-level metadata for indicator-macd
+# Auto-synced to PostgreSQL on push to main
+
+spec_id: indicator-macd
+title: MACD Technical Indicator Chart
+
+# Specification tracking
+created: 2026-01-07T16:13:17Z
+updated: null
+issue: 3181
+suggested: MarkusNeusinger
+
+# Classification tags (applies to all library implementations)
+# See docs/reference/tagging-system.md for detailed guidelines
+tags:
+  plot_type:
+    - line
+    - bar
+    - indicator
+  data_type:
+    - timeseries
+    - numeric
+  domain:
+    - finance
+    - trading
+  features:
+    - technical-analysis
+    - momentum
+    - crossover
+    - multi-component