Report coarse local execution capabilities

[luca-ctx]

Summary

This adds a versioned, coarse execution-capability snapshot to the existing CLI analytics request so we can prioritize compatibility and performance work across the machines people use.

• reports bucketed available parallelism and host-visible memory
• reports an allowlisted CPU vector tier and passive accelerator candidate
• sends the snapshot at most once per schema version using private local state
• respects the existing analytics opt-out, dry-run, and command eligibility behavior

The snapshot does not include component names, serial numbers, hardware IDs, exact memory sizes, utilization, or benchmark results. Accelerator checks do not load a runtime or model.

Validation

• cargo test --workspace --locked
• cargo clippy --workspace --all-targets --locked -- -D warnings
• cargo check -p ctx --target x86_64-pc-windows-gnu --locked
• cargo check -p ctx --target x86_64-unknown-freebsd --locked
• exact 11-target Bazel public smoke gate
• native Linux and Apple Silicon payload smoke tests
• independent adversarial privacy, security, concurrency, and portability review

[luca-ctx]

Validation complete on the rebased head (cd72b762):

• full cargo test --workspace --locked passed
• strict workspace clippy passed
• Windows GNU and FreeBSD cross-checks passed
• exact Buildkite public smoke gate passed locally: 11/11 targets
• independent adversarial review found no remaining P0-P2 issues

The repository webhook accepted the push and pull-request events, but no remote Buildkite check-run/status was published back to GitHub for this branch.