perf(diagnostics): bound RPC latency aggregation

[beruro]

Summary

• bound RPC duration aggregation cardinality and preserve stable buckets
• sanitize runtime counters before persistence/submission
• retain only the diagnostics detail needed for performance investigation
• cover bucket edges and queue/sanitization behavior

Independence

This 8-file PR is independent of both the #512 session stack and the #562 async stack.

Validation

• diagnostics Vitest: 4 passed
• pnpm typecheck and changed-file ESLint
• cargo test -p org2 usage_diagnostics: 7 passed
• cargo check -p org2
• rustfmt check on changed Rust files
• git diff --check origin/develop...HEAD

Performance guard

Aggregation has explicit cardinality bounds; raw/path-like values remain sanitized; queue rows transition from unsent to sent without retained duplicate payloads.