Task: Add sprint velocity bar charts to agile board

The top of the agile board shows two bar charts side by side — one for tasks completed per sprint day, one for commits per sprint day — so the team can see sprint velocity at a glance without leaving the dashboard.

• Two bar charts render at the top of the board above the story table.
• X-axis: sprint days 1–7 (derived from #+start_date / #+end_date in the current sprint's sprint.org).
• Chart A: count of tasks whose #+todo: transitioned to DONE on each sprint day (sourced from graphdata.json task nodes).
• Chart B: commit count per sprint day (sourced from the git log data already in graphdata.json or fetched at build time).
• Days beyond today render with a lighter colour (future / not yet elapsed).
• Both charts use the same x-axis scale so visual comparison is easy.
• If #+end_date is absent, a single combined chart falls back to showing the last 14 days of activity instead.

1. Confirm that graphdata.json carries enough data to drive both charts:
   • Task nodes: does each task carry a done_date or is it inferrable from git history? Investigate what the Emacs export puts in the JSON.
   • Commit data: check whether graphdata.json includes commit history, or whether it needs to be added as a new top-level key.
2. Extend the graphdata.json export (in the Emacs site-build script or a separate compass command) with:
   • sprint.start_date / sprint.end_date for the active sprint.
   • commits_by_day: array of {date, count} for the sprint window.
   • Task done-date is likely already present; verify or add.
3. In ores.org-js, add a VelocityCharts component:
   • Reads sprint.start_date / sprint.end_date to build the day axis.
   • Renders two <canvas> bar charts (Chart.js is already a dependency if the timeline view uses it; otherwise add it).
   • Mount at the top of the board view, above the story table.
4. Style: match existing dashboard palette; future days in rgba(...) with 40% opacity.

Two charts rather than one combined chart keeps each y-axis meaningful — tasks and commits have different magnitudes and units, so overlaying them on a dual-axis chart is harder to read than two narrow side-by-side bars.

Abandoned. Blocked on Stamp sprint end date (#+end_date not yet written by compass) and requires Chart.js integration and Emacs export changes — out of scope for this sprint. Captured for the product backlog.