[TASK] restore subcommand + session-id validation

[kirich1409]

Context

devsweep restore --session <id>. Validates id via regex + realpath boundary; handles conflicts via --overwrite / --suffix. Reads manifest + JSONL directly (no cache).

Acceptance criteria

• AC-6a, AC-6b, AC-26 pass.
• AC-27 passes (path-traversal rejected).

Files to touch (estimate)

best-effort estimate; agent refines during implementation

Implementation notes

n/a

Dependencies

• Blocked by [TASK] main.swift composition root #66
• Blocked by [TASK] Input validation grammars (S14) #48
• Blocked by [TASK] Session manifest lifecycle (.partial -> .json) + startup reconcile #53

Safety checklist

See .github/ISSUE_TEMPLATE/task.yml — tick applicable invariants in the issue if any destructive path is touched.

Definition of Done

• Acceptance criteria satisfied and verifiable
• Tests added or updated
• No build / lint / test regressions
• Self-review against research-report invariants
• Code review approved