Richer dashboard + redo screenshot with realistic synthetic data

[ialchemist-dev]

Context

The current dashboard (glance/dashboard/build.py) renders flat key/value
panels — fine as a v0.1 contract, but a real glance-worthy dashboard
should look more like:

• Per-day bar chart of productivity hours over the last 14 days
• Mood heatmap (day × hour grid, color-coded by label)
• Top mood-labels with frequency bars
• MIT done/open dots aligned with the daily axis
• Reminder list with due-date emphasis
• Build-time freshness badge with "X minutes ago" relative timestamp

Tasks

• Extend the component contract so stats.py can return chart-ready
  time series, not just summary key/values (without breaking the
  simple summary path).
• Upgrade dashboard/build.py template + per-panel renderers (charts
  via inline SVG; no JS framework dependency).
• Apply the richer renderers to mood, mit, reminder, diary panels.
• Re-shoot docs/screenshot.png from a fresh user's perspective with
  ~2 weeks of realistic synthetic data covering all four components,
  including diary (currently disabled in the screenshot build because
  no OAuth in CI).

Why deferred

v0.1 ships with the simple-summary contract so the component framework
and scaffolder pipeline can be validated independently of dashboard
aesthetics. This is a v0.2 follow-up.