feat(node): add public all-wallet balance export (#8359)

[tariqtharwat-OPS]

Summary

Closes #8359 by adding a public, read-only, paginated GET /api/balances/export endpoint for complete distribution analysis.

This is a clean implementation from current main that addresses the unresolved maintainer findings on #8361:

• pagination occurs in SQL before ledger aggregation; duplicate identifiers are not collapsed
• bounded per-page cache is keyed by current epoch, limit, and offset
• cache is bypassed when the epoch cannot be determined
• dedicated, thread-safe, bounded per-IP rate limiter with Retry-After
• exact wallet classification: bcn_*, native RTC + 40 hex, otherwise hosted_handle
• founder detection uses the founder_ prefix
• explicit modern, legacy, and mixed-schema handling without coercing null balances to zero
• missing optional ledger yields last_activity: null; malformed ledger schema fails visibly
• public identity/activity disclosure is documented in the API catalog and OpenAPI spec

Response schema

Each item contains:

• wallet
• balance_rtc
• is_founder
• kind
• last_activity

Pagination metadata includes count, total, limit, offset, and epoch.

Verification

• python -m py_compile node/rustchain_v2_integrated_v2.2.1_rip200.py node/tests/test_api_balances_export.py
• python -m pytest -q node/tests/test_api_balances_export.py node/tests/test_api_miners_rate_limit.py node/tests/test_admin_rate_limit.py node/tests/test_integrated_openapi_balance_schema.py
  • 21 passed, 9 subtests passed
• python docs/api/validate_openapi.py docs/api/openapi.yaml
  • No errors or warnings
• git diff --check

The two failures in test_public_api_disclosure.py were reproduced unchanged on upstream main; they predate and are unrelated to this endpoint.

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