spec: add candlestick-volume specification (#3074)

## New Specification: `candlestick-volume`

Related to #3068

---

### specification.md

# candlestick-volume: Stock Candlestick Chart with Volume

## Description

A professional candlestick chart combining OHLC (open, high, low, close)
price data with volume bars in a synchronized lower pane. The dual-pane
layout presents price action in the main chart with corresponding
trading volume below, sharing a common time axis. This format is the
standard for technical analysis platforms, enabling traders to correlate
price movements with trading activity and identify volume-confirmed
trends or reversals.

## Applications

- Analyzing stock price movements alongside trading volume to confirm
breakout patterns
- Identifying divergences between price trends and volume for potential
reversal signals
- Evaluating cryptocurrency or forex pairs with volume context for
entry/exit decisions

## Data

- `date` (datetime) - Trading date or timestamp for each period
- `open` (numeric) - Opening price at the start of the period
- `high` (numeric) - Highest price during the period
- `low` (numeric) - Lowest price during the period
- `close` (numeric) - Closing price at the end of the period
- `volume` (numeric) - Number of shares or units traded during the
period
- Size: 30-120 periods for clear visualization without overcrowding
- Example: Daily OHLC data with volume for a stock over 60 trading days

## Notes

- Use a shared x-axis between the candlestick and volume panes with
proper date formatting
- Volume bars should use the same up/down color scheme as candlesticks
for visual consistency
- The price pane should occupy roughly 70-75% of the vertical space,
volume pane 25-30%
- Include a crosshair or cursor that spans both panes for precise
price/volume reading
- Grid lines should be subtle and aligned across both panes

---

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plots/candlestick-volume/specification.md

@@ -0,0 +1,30 @@
+# candlestick-volume: Stock Candlestick Chart with Volume
+
+## Description
+
+A professional candlestick chart combining OHLC (open, high, low, close) price data with volume bars in a synchronized lower pane. The dual-pane layout presents price action in the main chart with corresponding trading volume below, sharing a common time axis. This format is the standard for technical analysis platforms, enabling traders to correlate price movements with trading activity and identify volume-confirmed trends or reversals.
+
+## Applications
+
+- Analyzing stock price movements alongside trading volume to confirm breakout patterns
+- Identifying divergences between price trends and volume for potential reversal signals
+- Evaluating cryptocurrency or forex pairs with volume context for entry/exit decisions
+
+## Data
+
+- `date` (datetime) - Trading date or timestamp for each period
+- `open` (numeric) - Opening price at the start of the period
+- `high` (numeric) - Highest price during the period
+- `low` (numeric) - Lowest price during the period
+- `close` (numeric) - Closing price at the end of the period
+- `volume` (numeric) - Number of shares or units traded during the period
+- Size: 30-120 periods for clear visualization without overcrowding
+- Example: Daily OHLC data with volume for a stock over 60 trading days
+
+## Notes
+
+- Use a shared x-axis between the candlestick and volume panes with proper date formatting
+- Volume bars should use the same up/down color scheme as candlesticks for visual consistency
+- The price pane should occupy roughly 70-75% of the vertical space, volume pane 25-30%
+- Include a crosshair or cursor that spans both panes for precise price/volume reading
+- Grid lines should be subtle and aligned across both panes

plots/candlestick-volume/specification.yaml

@@ -0,0 +1,31 @@
+# Specification-level metadata for candlestick-volume
+# Auto-synced to PostgreSQL on push to main
+
+spec_id: candlestick-volume
+title: Stock Candlestick Chart with Volume
+
+# Specification tracking
+created: 2025-12-31T13:39:18Z
+updated: null
+issue: 3068
+suggested: MarkusNeusinger
+
+# Classification tags (applies to all library implementations)
+# See docs/concepts/tagging-system.md for detailed guidelines
+tags:
+  plot_type:
+    - candlestick
+    - bar
+    - subplot
+  data_type:
+    - timeseries
+    - numeric
+    - ohlc
+  domain:
+    - finance
+    - trading
+  features:
+    - multi-pane
+    - volume
+    - synchronized
+    - interactive