🧹 fix(core): integrate validate_safe_path in core path operations

[Cylae]

Rationale

The public function validate_safe_path in server_manager/src/core/validate.rs provides path traversal protection (.. rejection). By integrating validate_safe_path directly into core filesystem and locking functions (atomic_write, ProcessLock::acquire, and Journal::open_or_create), system-wide path safety is enforced while resolving unused code concerns.

Changes

• server_manager/src/core/atomic_io.rs: Validates destination paths via validate_safe_path in atomic_write.
• server_manager/src/core/lock.rs: Validates lockfile paths via validate_safe_path in ProcessLock::acquire.
• server_manager/src/core/journal.rs: Validates journal file paths via validate_safe_path in Journal::open_or_create.

Verification

• Executed ./verify.sh covering cargo fmt, cargo clippy, cargo test, cargo deny, and cargo audit. All checks passed cleanly.

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PR created automatically by Jules for task 10011583263562090100 started by @Cylae

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