init: cryptographic append-only ledger

ASSURANCE.md

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+# Assurance Run — 2025-12-18
+
+- Commit: _not tracked (civilization-ledger is a workspace directory, not a git repo)_
+- Toolchain: `rustc 1.92.0 (ded5c06cf 2025-12-08)`, `cargo 1.92.0 (344c4567c 2025-10-21)`
+
+| Check | Status | Notes |
+| --- | --- | --- |
+| `cargo fmt --check` | ✅ | Formatting already matched default rustfmt. |
+| `cargo clippy --all -- -D warnings` | ❌ | Multiple Clippy findings (needless range loops in `attestation.rs`/`receipt.rs`, redundant closures in `merkle.rs`, `manual_div_ceil`, `manual_is_multiple_of`, etc.). |
+| `cargo test` | ✅ | CLI + `ledger-core` integration/unit tests all passed. |
+
+No files were changed during this pass.