Fix all 23 svelte-check warnings; enforce zero-warnings in check

Commit notes

- ShareActivityFeed/ShareComments captured props once at init (state_referenced_locally) — real staleness bugs: switching the selected share link/token after mount kept querying the old one. The two query hooks now take getters (the convention createAllShareActivityQuery already used) so the prop is read reactively. - WorkspaceSwitcher had a <button> nested in a <button> (invalid HTML, SSR hydration mismatch); the manage affordance is now a span with button role, keyboard handling, and an aria-label. - PackOrganizer's four autofocus attributes replaced with a use:focusOnMount action (focus only when the user opens the inline edit, not at document load). - Label/control associations via for/id (ShareDialog, SharePermissions, UploadLinkForm); heading-only labels demoted to spans; color swatch buttons got aria-labels; the placement-modal backdrop uses the target===currentTarget pattern instead of an interactive inner div. - svelte-check now runs with --fail-on-warnings so new warnings block.

[private session redacted]