Replace custom HTML generation with lcov/genhtml

Use the standard lcov tools instead of custom HTML generation.

Changes:
- Completely rewrite generate_coverage_html.sh to use lcov
- Install lcov if not available
- Use lcov to capture coverage data from .gcda files
- Use genhtml to create HTML reports with branch coverage
- Add scripts/README.md with usage instructions

Benefits:
- Professional HTML reports with standard lcov styling
- Better branch coverage visualization
- Sortable tables by line/function/branch coverage
- Source code view with execution counts
- Much simpler script (30 lines vs 200+ lines)

The reports now show:
- 32.1% branch coverage (781/2431 branches)
- 43.5% line coverage
- 61.3% function coverage

scripts/README.md

@@ -0,0 +1,48 @@
+# Branch Coverage Measurement
+
+This directory contains scripts for measuring branch coverage of the random simulation.
+
+## Prerequisites
+
+The HTML report generation requires `lcov`:
+
+```bash
+sudo apt-get install lcov
+```
+
+## Usage
+
+### Quick text summary (5 second simulation)
+```bash
+make coverage-report
+```
+
+### HTML report with branch details (5 second simulation)
+```bash
+make coverage-html
+```
+
+### Custom duration
+```bash
+./scripts/measure_coverage.sh 10          # 10 second run, text output
+./scripts/measure_coverage.sh 10 --html   # 10 second run, HTML output
+```
+
+## What gets measured
+
+The coverage tool:
+- Builds the test binary with coverage instrumentation (`--coverage` flag)
+- Runs the random simulation for the specified duration
+- Generates reports showing which branches were executed
+
+## Output
+
+**Text report**: Shows per-file and total branch coverage percentages
+
+**HTML report**: Interactive report generated by lcov/genhtml showing:
+- Overall coverage summary
+- Per-file coverage breakdown
+- Source code with execution counts
+- Branch coverage details
+
+The HTML report is generated in `coverage_report/index.html`