feat(logstats): export observed schedule timing - #1250

Summary

• Extend logstats schema v2 with per-stage timing and bounded p50/p95 estimates.
• Export representative typical and worst CopperList execution traces.
• Exclude carried-forward timestamp clusters and report residual timing separately.
• Detect overlaps between recorded process intervals sharing declared resource targets.
• Keep DAG logstats loading compatible with schema v1 and v2.

Stack

PR 2 of 4.

• Depends on fix(logstats): resolve config features and mission defaults #1249.
• Next: feat(plan): render observed execution timing #1251.
• Final: feat(dx): add plan-log workflows #1245.

Verification

• Rust formatting check passed for all changed Rust files.
• Diff whitespace check passed.
• Full workspace verification is deferred to CI because the local checkout is missing the optional sibling cu-vitfly path dependency.