IM-2221 add auto-fill template workflow

[LandonS23]

Description

Adds a GitHub Action that automatically populates PR descriptions when a PR is opened.

What it does

• Extracts Jira ticket from branch name (e.g., feat/IM-123-...) and links it
• Detects change type from branch prefix and checks the appropriate box
• Uses Claude to generate a description and testing suggestions from the diff
• Falls back to file list if Claude API is unavailable

Change type detection

Type	Branch prefix
Bug fix	fix/, bugfix/, hotfix/
New feature	feat/, feature/
Refactor	refactor/
Documentation	docs/
Chore	chore/, deps/, dependencies/
Breaking change	(manual — no auto-detect)

Uses existing ANTHROPIC_API_KEY secret.

Ticket

IM-2221

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactor (code change that neither fixes a bug nor adds a feature)
• Documentation update
• Chore (dependency updates, config changes, etc.)

[LandonS23]

Workflow — Now only fills sections that are empty:

✅ Checks if Description is empty (just comment) → fills with Claude
✅ Checks if Ticket is empty → fills from branch name
✅ Checks if no Type checkbox is checked → auto-checks based on branch prefix
✅ Checks if Testing Done is empty → fills with Claude suggestions
✅ Preserves any content the user already wrote