fix(schema): rename explorer pricing to price (#2481)

[Larslllllll]

Summary

Unblocks approved DBIP #2481 by aligning the explorer schema with the shared price column before the main-branch CSV rename.

Changes

• tools/schema.json: rename explorer property pricing to price
• tools/schema.json: rename the matching required key
• meta/columns.json: remove the now-redundant explorer-only pricing metadata; shared price metadata already exists

Validation

• Both JSON files parse successfully
• Every explorer required key is present in explorer properties
• price exists in schema and metadata; pricing no longer exists there
• git diff --check passes

This intentionally targets json-tools first. After merge, a separate data PR against main can perform the header-only rename without the CI ordering failure described in #2481.

Payout

Approved DBIP #2481: 10 USDC to 0x06f44f4839fd5df4f4670036d028b29dec939363.