Apply the category-browsing rubric consistently to ProteinTraitsMech #403

The website-feature table rates ProteinTraitsMech category browsing as present, although its own note says the landing links open filtered browser views. The catalogue explicitly defines filter-only category browsing as partial; CommunityMech is already rated partial on that basis.

An independent live check found 95 category, source and axis links on the ProteinTraitsMech landing page, all opening browse.html hash filters. For example, browse.html#cat=SEQ_DOMAIN displays one active filter and 75,935 filtered records within the common browser.

Change ProteinTraitsMech's category_browse verdict to partial, explain the landing-link behavior in its evidence note, and regenerate the website-feature table and totals. This corrects application of the existing rubric; it does not claim a new website regression.

Priority: P3. Resolution belongs in PR #399.