refactor: migrate Markdown to AsciiDoc

.security/CRYPTO_NOTICE.adoc

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+== Cryptographic Hash Policy
+
+=== Current Status
+
+This repo uses MD5 or SHA1 in some files.
+
+=== Policy
+
+* *NEVER* use MD5/SHA1 for security purposes (passwords, signatures,
+integrity)
+* MD5/SHA1 is acceptable ONLY for:
+** Cache key generation (non-security)
+** Legacy format compatibility
+** File checksums (when not security-critical)
+
+=== Migration
+
+Replace security-critical usage: - `+md5(password)+` → `+argon2+` or
+`+bcrypt+` - `+sha1(signature)+` → `+sha256+` or `+sha384+` -
+`+md5(integrity)+` → `+sha256+`
+
+=== Files to Review
+
+Check files flagged by CI for MD5/SHA1 usage.

ARCHITECTURE.adoc

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+== Architecture
+
+=== Overview
+
+This repository follows a modular, maintainable architecture designed
+for clarity, scalability, and long-term sustainability.
+
+=== Directory Structure
+
+....
+.
+├── src/           # Source code
+├── tests/        # Test suites
+├── docs/         # Documentation
+├── scripts/      # Utility scripts
+├── config/       # Configuration files
+├── LICENSE       # License file
+├── LICENSES/     # Full license texts
+└── README.adoc   # Project documentation
+....
+
+=== Design Principles
+
+* *Separation of Concerns*: Each module has a single responsibility
+* *Testability*: Code is written to be easily testable
+* *Documentation*: All public APIs are documented
+* *Configuration*: Environment-specific settings are externalized
+
+=== Dependencies
+
+* External dependencies are minimized and clearly declared
+* Version pinning is used for reproducibility
+
+=== Security Considerations
+
+* Sensitive data is never committed to the repository
+* Secrets are managed through environment variables or secure vaults
+* Regular dependency audits are performed
+
+=== Maintainability
+
+* Code follows consistent style guidelines
+* Pull requests require review and CI checks
+* Issues and discussions are tracked transparently
+
+'''''
+
+_Last updated: 2026-07-18_