[Tiancheng-Xu]

Closes #473

The experiments table showed when the latest run started but not how long it took. This adds elapsed duration beside the existing relative timestamp. Finished runs use endedAt; active runs update every second.

Current main has been merged into this branch, and the embedded UI bundle has been regenerated to resolve the generated-asset conflicts.

Test plan

• corepack pnpm@10.16.1 build in ui (i18n lint, typecheck, Vite build)
• node --test --experimental-strip-types --test-reporter=spec ui/tests/*.test.mjs (210 passed)
• node ui/scripts/check-styles.mjs
• node --test scripts/dev-slot.test.mjs (9 passed)
• python3 scripts/test_release_notes.py (6 passed)
• cargo fmt --all --check and cargo fmt --manifest-path windows/launcher/Cargo.toml --check (Rust 1.95.0)
• Repeat Vite build produced no changes to the committed UI bundle
• git diff --check
• Rust clippy/build/tests and platform CI remain to be verified upstream; no Rust source changes are introduced by this PR relative to current main.

[Tiancheng-Xu]

Merged current main and regenerated the embedded UI bundle in 2302d92b493ba233c4ce54412cc7b59fd6de14b9; the merge conflicts are now resolved.

Fresh verification: 210 UI tests, 9 dev-slot tests, 6 release-note tests, UI style lint, i18n/typecheck/build, both Rust formatting checks, and an unchanged repeated Vite bundle build. The test plan now records these results and explicitly leaves Rust clippy/build/tests and platform CI pending. Keeping this draft until those checks can be verified.