feat: round-15 abstractions — parallel_for_each streaming fan-out

.hermes/plans/mytheclipse-round15-spec.md

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+# Implementation Spec: Round 15 — COMPLETE
+
+## New Feature
+
+### parallel_for_each (mytheclipse-core, resiliency)
+File: `crates/mytheclipse/src/parallel_map.rs`
+- Streaming bounded parallel fan-out: runs `f` over each item with bounded
+  concurrency WITHOUT materializing the whole input first (unlike parallel_map
+  which collects up front)
+- Bounded mpsc channel (capacity = concurrency*2) + producer task + worker
+  pool sharing the receiver behind a tokio Mutex — inherent backpressure
+- Errors aggregated into AggregateError (drain-first)
+- Bounds: I: IntoIterator + Send + 'static, I::IntoIter: Send (producer task
+  is tokio::spawn -> needs Send + 'static)
+- 1 test (processes all 5 items)
+- Also fixed: cleaned unused Arc/Duration imports in worker_rate_limited.rs
+  (round-10 leftover)
+
+## Files
+- modified: core/src/parallel_map.rs (+parallel_for_each)
+- core/lib.rs: export parallel_for_each
+- queue/src/worker_rate_limited.rs: remove unused imports
+
+Build: 0 errors. Tests: 0 FAILED (101 core pass). Clippy: 0 new warnings.