feat: multi-format report generation (JSON, CSV, HTML, Markdown)

[kristopherjturner]

Overview

Implement report generation in multiple output formats (JSON, CSV, HTML, Markdown) from the normalized result schema collected during test runs. Reports should be self-contained and shareable with stakeholders.

Scope

• src/reporters/json_reporter.py — Machine-readable JSON result dump
• src/reporters/csv_reporter.py — Tabular CSV for Excel/Power BI import
• src/reporters/html_reporter.py — Self-contained HTML report with embedded charts
• src/reporters/markdown_reporter.py — Markdown summary for GitHub PR comments or wiki
• Comparison mode: diff two run reports to highlight regressions

Acceptance Criteria

• All four report formats generated from a single run result set
• HTML report includes charts (latency CDF, IOPS over time, throughput over time)
• Comparison mode flags metrics exceeding configurable regression threshold
• Reports stored in reports/ with session timestamp and tool name
• Report format selection configurable in YAML

Dependencies

• Parent Epic: [Epic] Load Testing Toolkit Full Build-Out #8
• Core framework: feat: core framework modules (session, collector, logger, reporter) #10

Priority Note

Priority/medium — reports are useful but do not block test execution.