i18n(ru): pluralize Lab Book marker and reading counts

[kavemang]

What this PR does

Russian Lab Book count labels currently use the many form for every count, for example 2 измерений and 2 маркеров. Convert four single-count labels to CLDR one/few/many/other: the two marker/reading summary variants, the reading-history subtitle and the insufficient-variation message.

English singular/plural branching excludes numeric 1 from two of these keys, but Russian still needs their one form for 21 and similar counts. All count placeholders and existing noun choices are preserved. The keys exist only in the main catalog.

Only four Russian entries change. Other locales, import parsing, stored readings, correlation math, layout and Android independent resources are unchanged. Multi-count strings and other #573 counts are outside this small batch.

Draft for native Russian review requested by the issue and manual Lab Book display checks including 2, 5, 11, 21, 22 and 25.

Type of change

• Bug fix

How it was tested

• Focused JSON comparison: exactly four ru entries changed, all other catalog content and single count arguments preserved.
• Local diff-scoped i18n against origin/main, global hygiene and whitespace passed.
• Full local Tools discovery: 338 tests passed, zero failures, 178.548 seconds.
• Apple CI: universal macOS and iOS Simulator SDK builds/String Catalog compilation succeeded. StrandTests actually ran 2,269 tests, two skipped, zero failures.
• Tools CI: 50 parity repository-acceptance, 2 R-R contract, 153 core Tools and 234 linux-capture tests passed.
• Android CI: APK build succeeded; unit-test task FROM-CACHE, no fresh Android execution claimed. Android unchanged.
• Stable exact-head CI roster: six checks, all successful, including i18n and hygiene.
• Linux cannot build Apple targets; actual upstream SDK builds establish compile coverage. No native approval, runtime layout/VoiceOver or hardware validation claimed.

Checklist

• Existing UI/design tokens only; catalog-only change
• No new dependency, frame bytes, generated artifacts or secrets
• Follows docs/CONTRIBUTING.md

Related issues

Refs #573