feat(wallets): keyExportFormats schema, column metadata and validation (DBIP #3725)

[foxxx009]

Closes #3725 (tools side)

Problem

The keyExport boolean cannot distinguish what can actually be backed up or migrated: an account private key, a mnemonic and an encrypted application backup are different artifacts.

Changes

• tools/schema.json: optional keyExportFormats property on wallets — JSON array or null, items restricted to the initial enum encrypted-backup/mnemonic/raw-private-key, uniqueItems: true.
• meta/columns.json: keyExportFormats metadata (arrayPopover, security group, searchableMultiSelect filter).
• tools/csv_to_json.py: validate_key_export_formats() — rejects nonarrays, unknown/case-mismatched names and duplicates, enforces canonical alphabetical ordering; wired into canonical offers and every expanded network listing.

Validation covered (per DBIP #3725 §Acceptance)

• JSON array validation, allowed values, uniqueness, canonical sorting
• NULL (not yet verified) and [] (explicit review found none) both accepted
• array preserved in generated JSON and normal offer/listing inheritance
• validate_csv.py → csv_to_json.py → validate.py all green locally

The existing keyExport boolean is untouched (no rename, no bulk rewrite). Data side: paired PR adds the column to the 92 wallet tables and seeds a single verified Algorand cell (Pera).

Rewards address: 0x2409b47a530be3831158f10b08ac93f7d08c1ff2