feat: Documentation Overhaul, Security Hardening & Code Style Enforement

[Kaylahray]

feat: Documentation Overhaul, Security Hardening & Code Style Enforcement

Closes #97
Closes #98
Closes #99

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What changed and why

This PR consolidates three medium/high priority issues into a single,
atomic improvement across documentation, security, and code quality.
Each section maps directly to its issue acceptance criteria.

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#97 — Outdated Developer Documentation

File	Change
DEVELOPMENT.md	Full rewrite — versioned, reflects current system state
CONTRIBUTING.md	PR checklist, doc standards, versioning workflow added
docs/documentation-maintenance.md	New — formal quarterly maintenance process

• All new features are now documented
• Documentation versioning policy established
• Contribution guidelines updated with doc requirements

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#98 — Missing Security Documentation

File	Change
SECURITY.md	Overhauled — best practices, secure patterns, audit log
docs/threat-model.md	New — full STRIDE threat model with mitigations per asset
docs/incident-response.md	New — P0–P3 severity runbooks and escalation contacts
docs/security_pipeline.md	Expanded — CI audit trail, monitoring and alerting runbooks

• Security best practices guide: complete
• Threat model documented with mitigations
• Incident response procedures (P0–P3): complete
• Security documentation maintenance cadence: defined

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#99 — Inconsistent Code Style

File	Change
docs/code-style-guide.md	New — canonical Rust style guide for all PropChain contracts
clippy.toml	Tightened — security-critical and correctness lints enforced
rustfmt.toml	Pinned edition, uniform formatting across all crates
.pre-commit-config.yaml	Added cargo-audit and cargo-deny hooks
scripts/setup-pre-commit.sh	Auto-installs audit/deny tooling on dev setup
rust-toolchain.toml	Locked to stable with pinned components

• Code style standardised across all contracts
• Automated style + security checking on every commit via pre-commit hooks
• Code style guidelines: documented and enforced

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Checklist

• All acceptance criteria from Outdated Developer Documentation #97 satisfied
• All acceptance criteria from Missing Security Documentation #98 satisfied
• All acceptance criteria from Inconsistent Code Style #99 satisfied
• No breaking changes to contract logic
• CI-compatible (rustfmt + clippy configs are consistent)
• Docs cross-linked where relevant

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