Extend rust-performance with concurrency patterns (crossbeam, rayon, atomics)

[AlexMikhalev]

Parent Epic: #62

What

Add concurrency primitive patterns to rust-performance SKILL.md. Currently covers async but not lower-level concurrency.

Sections to Add

1. Lock-Free Data Structures -- crossbeam epoch-based reclamation, concurrent queues
2. Data Parallelism with Rayon -- par_iter(), parallel chunking, custom thread pools
3. Atomic Operations -- Ordering levels (Relaxed/Acquire/Release/SeqCst), when to use each
4. Thread Pool Configuration -- Custom stack sizes, thread naming, affinity
5. Cache Locality in Concurrent Code -- Avoiding false sharing, padding for cache lines

Source Reference

Section 8 (Concurrency Patterns) from RUST_SYSTEM_PROGRAMMING_BEST_PRACTICES.md

Disciplined Engineering Alignment

Phase	Skill	Concurrency Relevance
Research	disciplined-research	Profile existing code for parallelism opportunities; identify shared-state contention points
Design	disciplined-design	Specify concurrency strategy (rayon vs crossbeam vs atomics); document memory ordering requirements; design cache-friendly layouts
Implementation	disciplined-implementation	Implement lock-free structures with safety invariants per step; rayon integration as separate step from correctness
Verification	disciplined-verification	ThreadSanitizer on all concurrent paths; stress tests with loom for atomic ordering; benchmark parallel vs sequential
Validation	disciplined-validation	Validate throughput under production load patterns; verify no deadlocks/livelocks under sustained stress

The SKILL.md should note:

• During research: profile for Amdahl's law -- identify serial bottlenecks before parallelizing
• During design: specify memory ordering rationale for every atomic operation
• During verification: loom and TSan are mandatory for lock-free code

Relevance to Terraphim

Terraphim uses Aho-Corasick automata with parallel text processing. crossbeam and rayon patterns are directly applicable to search pipeline performance.

Acceptance Criteria

• SKILL.md updated with concurrency section including code examples
• crossbeam and rayon added to crate recommendations
• Benchmark template extended for concurrent workloads
• Disciplined workflow integration notes included