Improve the roadmap display on the project detail page

[komalharshita]

The roadmap timeline on /project/<id> currently shows plain text steps.
It would be more readable if completed-looking steps were visually distinct
from upcoming steps, and if the connecting line between dots used a dashed
style to imply progress rather than a solid line.

Expected Outcome:

• The connector line between roadmap dots is border-left: 2px dashed
  instead of solid
• The first roadmap dot uses a filled style (already done)
• All other dots use a hollow style (white fill, coloured border) to
  suggest they are future steps
• No JavaScript is required — this is CSS-only

Files to look at:

• static/style.css — the roadmap timeline section
• templates/project.html — the .roadmap-step structure