spec: add survival-kaplan-meier specification (#2449)

## New Specification: `survival-kaplan-meier`

Related to #2441

---

### specification.md

# survival-kaplan-meier: Kaplan-Meier Survival Plot

## Description

A Kaplan-Meier survival plot visualizes the probability of survival (or
event-free time) over a time period using a step function. It is the
standard method for estimating survival functions from time-to-event
data, handling censored observations where the event has not yet
occurred. The plot shows how survival probability decreases over time,
with optional confidence intervals and comparison between groups.

## Applications

- Medical research tracking patient survival rates after diagnosis or
treatment
- Reliability engineering analyzing time-to-failure for equipment or
components
- Customer analytics measuring time-to-churn or subscription retention
- Clinical trials comparing survival outcomes between treatment and
control groups

## Data

- `time` (numeric) - Time to event or censoring (e.g., days, months,
years)
- `event` (binary) - Event indicator (1 = event occurred, 0 = censored)
- `group` (categorical, optional) - Grouping variable for comparing
survival curves
- Size: 50-1000 observations
- Example: Clinical trial data with patient survival times and treatment
groups

## Notes

- Use step function (not smooth curves) to accurately represent discrete
event times
- Include 95% confidence intervals as shaded bands around the survival
curve
- Mark censored observations with tick marks on the curve
- When comparing groups, use distinct colors and include a legend
- Consider adding median survival time annotation and at-risk table
below the plot
- Log-rank test p-value can be included when comparing groups

---

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plots/survival-kaplan-meier/implementations/.gitkeep

@@ -0,0 +1,29 @@
+# survival-kaplan-meier: Kaplan-Meier Survival Plot
+
+## Description
+
+A Kaplan-Meier survival plot visualizes the probability of survival (or event-free time) over a time period using a step function. It is the standard method for estimating survival functions from time-to-event data, handling censored observations where the event has not yet occurred. The plot shows how survival probability decreases over time, with optional confidence intervals and comparison between groups.
+
+## Applications
+
+- Medical research tracking patient survival rates after diagnosis or treatment
+- Reliability engineering analyzing time-to-failure for equipment or components
+- Customer analytics measuring time-to-churn or subscription retention
+- Clinical trials comparing survival outcomes between treatment and control groups
+
+## Data
+
+- `time` (numeric) - Time to event or censoring (e.g., days, months, years)
+- `event` (binary) - Event indicator (1 = event occurred, 0 = censored)
+- `group` (categorical, optional) - Grouping variable for comparing survival curves
+- Size: 50-1000 observations
+- Example: Clinical trial data with patient survival times and treatment groups
+
+## Notes
+
+- Use step function (not smooth curves) to accurately represent discrete event times
+- Include 95% confidence intervals as shaded bands around the survival curve
+- Mark censored observations with tick marks on the curve
+- When comparing groups, use distinct colors and include a legend
+- Consider adding median survival time annotation and at-risk table below the plot
+- Log-rank test p-value can be included when comparing groups

plots/survival-kaplan-meier/metadata/.gitkeep

@@ -0,0 +1,33 @@
+# Specification-level metadata for survival-kaplan-meier
+# Auto-synced to PostgreSQL on push to main
+
+spec_id: survival-kaplan-meier
+title: Kaplan-Meier Survival Plot
+
+# Specification tracking
+created: 2025-12-29T22:39:04Z
+updated: null
+issue: 2441
+suggested: MarkusNeusinger
+
+# Classification tags (applies to all library implementations)
+# See docs/concepts/tagging-system.md for detailed guidelines
+tags:
+  plot_type:
+    - survival
+    - step
+    - line
+  data_type:
+    - numeric
+    - timeseries
+    - categorical
+  domain:
+    - healthcare
+    - statistics
+    - research
+    - engineering
+  features:
+    - basic
+    - confidence-interval
+    - censored-data
+    - comparison