feat(security): Port IronClaw security modules to workspace structure, fix merge conflicts

[Copilot]

feature/ironclaw-imports had merge conflicts with main because main restructured from a monolithic crate to a Cargo workspace while the feature branch was still based on the old layout.

Conflict resolutions

• Cargo.toml — Replaced old single-package manifest with workspace format matching main; added aho-corasick = "1.1" to [workspace.dependencies]
• src/lib.rs — Deleted; main removed this file during the workspace split (delete/modify conflict)

New files in workspace location (crates/rustyclaw-core/src/security/)

• leak_detector.rs — Aho-Corasick O(n) multi-pattern credential leak detection (IronClaw-inspired); replaces the inline LeakDetector/LeakResult stubs previously embedded in safety_layer.rs
• validator.rs — Input validation: length limits, null-byte detection, whitespace/repetition heuristics, forbidden-pattern matching, recursive JSON param validation
• safety_layer.rs — Updated to import from leak_detector and validator instead of carrying inline definitions
• mod.rs — Re-exports all public types from the new modules
• crates/rustyclaw-core/Cargo.toml — Adds aho-corasick.workspace = true

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