feat(import): add ticket import from Jira and GitHub Issues (PUNT-34)

[jmynes]

Summary

• Add Jira JSON/CSV and GitHub Issues JSON import parsers with auto-format detection
• Add API route POST /api/projects/[projectId]/import for batch ticket creation with label auto-creation
• Add Import tab in Project Settings with drag-and-drop file upload, ticket preview with select/deselect, and column targeting

Details

Parsers (src/lib/import/):

• Jira: Maps summary, description (including ADF), type (Story/Bug/Task/Epic/Sub-task), priority (Blocker->critical, etc.), status, resolution, labels, components, story points from both JSON and CSV formats
• GitHub: Maps title, body, state, labels; infers type/priority from well-known label names (e.g., "bug" label -> bug type, "p0" -> critical); excludes pull requests automatically
• Auto-detect: Heuristic detection based on JSON structure (key/fields -> Jira, state/number -> GitHub)

API (src/app/api/projects/[projectId]/import/route.ts):

• Atomic batch import in a single transaction
• Sequential ticket numbering from project max+1
• Creates missing labels with default colors
• Sprint history tracking for sprint-assigned imports
• SSE event emission for real-time sync

UI (src/components/projects/settings/import-tab.tsx):

• Drag-and-drop or click-to-browse file upload
• Preview stage with per-ticket select/deselect, type/priority badges, story points, label counts
• Target column selector
• Toggle for auto-creating missing labels
• Import progress and completion summary with warnings

Test plan

• Upload a Jira JSON export and verify tickets are parsed with correct field mapping
• Upload a Jira CSV export and verify the same
• Upload a GitHub Issues JSON (from gh issue list --json number,title,body,labels,state) and verify parsing
• Verify auto-detection picks the correct parser
• Deselect some tickets in preview, import, and verify only selected ones are created
• Verify labels are auto-created when toggle is on
• Verify imported tickets appear in the target column with correct numbering
• Verify the Import tab appears in Project Settings for users with settings permission

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