docs(templates): refine issue/pr templates for evidence patterns

[hkimw]

Summary

• Add evidence availability, maintainer decision, and timing/synthesis/board state fields to the issue templates.
• Add explicit evidence-state and stacking lines to the pull request template.
• Retire the older duplicate bug and feature template names so the issue picker uses the refined forms.

Evidence State

Evidence state: YAML parsed; markdown whitespace check clean; public wording scan clean; pre-push hook completed.

stacking on: none

Review

• Scope is bounded to issue and pull request templates.
• References the decision checklist pattern from [P0][SPEC] Resolve v002 datapath/spec mismatches before RTL changes pccx-FPGA-NPU-LLM-kv260#16 and the evidence-state pattern from docs(spec): resolve v002 quantization, K-drain, and DSP baseline pccx-FPGA-NPU-LLM-kv260#80.
• No repo settings, release, tag, or visibility changes.