docs: ROADMAP has stale category counts and lists search as planned though it shipped #69

Why it matters
ROADMAP.md is linked from the README as the place to start contributing. It contradicts the README and goes stale with every content PR.

Evidence

• ROADMAP.md:8 says "video (8 entries), animation (12) and environment (13)". main has 10/14/15, and PR Add 15 sources: video, animation, environment #58 makes it 13/17/18. site/sync-counts.mjs doesn't touch ROADMAP.md.
• ROADMAP "Planned" lists "Client-side search over the catalog, not only filters". README.md:142-144 says the site searches every entry ("Press / to search"), and ui: search matches inside words ("ui" matches "build", "art" matches "earth") #16 and ui: search is slow per keystroke (1s+ on throttled CPU) #17 shipped search.

Suggested approach

• Drop the hard-coded counts (link to the category table instead), or teach sync-counts.mjs to update that line.
• Move search to "Done", or reword the item if something more is meant (e.g. full-text search over entry bodies).
• Once PR Add 15 sources: video, animation, environment #58 merges, decide whether "Thin categories" is still a goal.

Done when
ROADMAP.md has no numbers that can drift and no items that the README says are done.