Tighten Decodex plugin skill budget

[yvette-carlisle]

Summary

• compact Decodex plugin skill entrypoints and move detailed routing/research method rules into shared references
• shorten plugin metadata/default prompts to reduce trigger cost
• preserve research promotion, Program Intake, label, commit, and land authority boundaries in references

Validation

• plugin-eval Decodex plugin: 100/A, 0 fail, 0 warn, active budget 2764 tokens
• plugin-eval all 15 Decodex skills: 100/A, 0 fail, 0 warn
• quick_validate.py all Decodex skills: pass
• git diff --check: pass
• plugin.json parse: pass