Add epic issues agent skill

[gatesn]

Summary

• add an epic-issues repo skill for working on Vortex epic issues
• document preserving checkbox state, linking PR numbers inline, and avoiding separate stack sections
• capture the stacked-epic workflow corrections from the current stats epic work

Tests

• inspected Markdown diff only; this is an agent-skill documentation change

[codspeed-hq]

Merging this PR will degrade performance by 16.89%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

❌ 6 regressed benchmarks
✅ 1210 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	new_bp_prim_test_between[i16, 32768]	120.7 µs	134.8 µs	-10.44%
❌	Simulation	new_bp_prim_test_between[i32, 16384]	95.1 µs	109.6 µs	-13.23%
❌	Simulation	new_bp_prim_test_between[i32, 32768]	141.5 µs	170.5 µs	-17.01%
❌	Simulation	new_bp_prim_test_between[i64, 16384]	115.5 µs	145 µs	-20.32%
❌	Simulation	new_alp_prim_test_between[f64, 16384]	127.5 µs	149.4 µs	-14.69%
❌	Simulation	new_bp_prim_test_between[i64, 32768]	178.3 µs	237.2 µs	-24.84%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing ngates/add-epic-issues-skill (d34f09f) with develop (b3e1673)}