fix: update export-meta.ts to use 'policy_type' instead of 'template'

[pyramation]

Summary

Updates the export-meta.ts config to use policy_type instead of template for the policy table field mapping. This aligns with the schema change in constructive-db PR #328 where the template column was renamed to policy_type in the metaschema_public.policy table.

Review & Testing Checklist for Human

• Verify constructive-db PR remove deps on psql, createdb, and dropdb and use node pg entirely #328 is merged first - This change depends on the policy table having a policy_type column instead of template. If merged before constructive-db, exports will fail.
• Confirm no other references to template for policies exist in this codebase that need updating

Notes

This is part of a larger refactoring effort to rename policy types to use PascalCase with Authz prefix (e.g., AuthzMembership, AuthzDirectOwner) and rename the column from template to policy_type.

Related PRs:

• constructive-db remove deps on psql, createdb, and dropdb and use node pg entirely #328: Main schema and code changes
• dashboard feat: add validateDeployment method for hash validation #105: Frontend policy type naming updates

Link to Devin run: https://app.devin.ai/sessions/14351ad5a39d46c9aa33be151e6977e4
Requested by: Dan Lynch (@pyramation)

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