Keep viewmodel animations shared with a shown weapon visible

[rndaom]

What broke

Some weapons reuse another weapon's animations in the class animation model. Soldier's Concheror uses the Shovel's draw, idle and swing animations; Engineer's Widowmaker shares an animation with the wrenches; spellbooks share swings with the Persian Persuader (Demoman) and Solemn Vow (Medic). Hiding one weapon hid those shared animations as well, so Keep melee visible left Soldier's Shovel invisible, and other classes lost some melee animations.

What changed

• The build hides an animation only when every weapon that uses it is hidden. A weapon left shown is always fully visible.
• Under each class, the builder names hidden weapons that stay partly visible because of this (for example, "Concheror stays partly visible: it shares animations with Shovel.").
• The catalog identity includes the rule version, so packs built before this change read as outdated. Their choices come back as an unbuilt draft with a one-line note to build again.
• A selection where every hidden animation is shared with a shown weapon is refused with a clear error.
• The browser preview catalog gains a small Soldier sample with the Concheror/Shovel overlap.
• Guide, architecture and changelog updated.

Checks

• cargo fmt --check, cargo clippy -D warnings, new resolution tests in viewmodel_group_selection.
• pnpm check, pnpm test (new UI tests for the outdated-pack draft and the partly-visible line), tsc --noEmit.
• Resolved a Keep-melee-visible selection against a real TF2 install: no melee animation is hidden for any class.
• Checked the Soldier view in the browser preview.