Refresh current docs and make native timing checks overflow-safe

[Views2k]

Current documentation still describes older supported builds, update timing, and the earlier WPF-only rendering path. Refresh it to match the shipped application, retain the current release and Runs guidance in the README, and point older announcements to the existing release history. Native hardware-GPU contracts remain a required manual release gate, explicitly separate from CI and installer builds.

Three native test assertions also add signed 64-bit timing values before comparing them with a total. Replace those additions with guarded subtraction that rejects negative components and bounds every subtraction. Compile-time cases cover zero, exact fit, signed limits, overflowing sums, and negative inputs. Existing count, duration, and status assertions remain intact.

Validation:

• Repository policy and whitespace checks pass; all 39 affected local documentation links/anchors resolve.
• The timing predicate matched an independent arbitrary-precision sum oracle for 20,736 boundary combinations and 10,000 seeded random cases, with checked signed arithmetic reporting no overflow.
• All README image/demo markup and tracked image bytes are unchanged. Runtime code, workflows, dependencies, installer behavior, and application version are unchanged.
• Native C++ compilation and hardware-GPU contracts were not run locally because this VM lacks the required toolchain. The normal required Build and test / Build installer checks must pass before merge. This maintenance PR does not publish an application release.

Closes #56.