Match JavaScript attention ledger semantics in Python verifier

[aruintelligence]

What changed

• Replay attention charges using binary64 arithmetic, including rounding after each addition, so Python accepts signed JavaScript receipts whose cumulative total crosses 2**53.
• Match Object.is for ledger balances: reject a boolean substituted for a number and distinguish -0 from +0 where JavaScript does. Retain negative zero when parsing raw integer tokens and accept it in fields where JavaScript Number.isInteger does.
• Add four signed cross-runtime cases, including a re-signed malformed ledger whose capsule hashes and signature remain valid, plus document the evidence boundary. Ignore generated Python bytecode.

Reproduction

Before this patch, JavaScript verified a signed receipt with attention charges [9007199254740991, 1, 1] and final total 9007199254740992, but Python rejected its ledger. Conversely, Python reported verified: true for a correctly re-signed receipt with remaining: true where JavaScript rejected the ledger.

Checks

• node --test: 797 passed
• node scripts/check-evidence-capsule-python.mjs: 36 passed
• node scripts/check-http-exchange-python.mjs: 28 passed
• Archive, migration, shard, drill, repair, placement, API stability, upgrade, and local link checks passed

These are project-authored synthetic tests of verifier behavior, not independent validation or a claim about human outcomes.