Spec Kit 0.3.0 upgrade for scripts, agents, and templates

[brooke-hamilton]

Summary

Upgrades the Spec Kit tooling to version 0.3.0, updating bash and PowerShell scripts, GitHub Copilot agent definitions, and spec templates.

Changes

Agent updates (.github/agents/)

• Minor updates to speckit.analyze, speckit.clarify, and speckit.constitution agents
• Significant rework of speckit.implement, speckit.plan, speckit.specify, speckit.tasks, and speckit.checklist agents

Bash scripts (.specify/scripts/bash/)

• Reformatted all scripts with shfmt
• Updated common.sh with expanded utility functions
• Reworked check-prerequisites.sh, create-new-feature.sh, setup-plan.sh, and update-agent-context.sh

PowerShell scripts (.specify/scripts/powershell/)

• Updated common.ps1, check-prerequisites.ps1, create-new-feature.ps1, setup-plan.ps1, and update-agent-context.ps1

Templates and configuration

• Added .specify/init-options.json recording Spec Kit 0.3.0 init settings
• Added .specify/templates/constitution-template.md for project constitutions
• Updated .specify/templates/plan-template.md with corrected links and expanded project type options