Task 455: Fix Episode Parser to Merge Multiple timeseries-charts Blocks

Status: DONE

Summary

The episode MDX parser (episode-mdx-parser.ts) overwrites timeSeriesCharts when encountering multiple timeseries-charts: fenced blocks — later blocks silently replace earlier ones. This is error-prone and was encountered in Task 454 when adding navigation error charts to EP03.

The fix is to merge (concatenate) charts from all blocks rather than overwriting.

Impact

• Currently, all episodes must put all timeseries charts in a single block
• This makes adding charts to specific analysis sections awkward — charts must be defined far from the prose that references them
• The summary parser (mdx-parser.ts) handles timeseries: with single-chart blocks, which is more flexible

Plan

1. Modify episode-mdx-parser.ts to append rather than overwrite for timeseries-charts
2. Add test verifying multiple blocks are merged
3. Consider doing the same for diagrams and glossary if they have the same issue