fix(hugo): ignore non-data files in data/metrics/ for Hugo build (#165)

The directory mount 'data/metrics' loads all files as Hugo data. copilot-transcript.md (markdown) and token-usage.jsonl (jsonl) are not valid Hugo data formats and broke the build with: ERROR error building site: failed to load data: unmarshal of format "" is not supported The previous ignoreFiles pattern 'data/metrics/' did not actually match — Hugo's ignoreFiles regex needs explicit file patterns. Only cost-summary.json is used by layouts/shortcodes/cost-dashboard.html. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>