feat: add session deletion with per-provider cleanup and path safety
Add delete_session Tauri command dispatching to provider-specific deletion
logic for all 5 providers (Claude, Codex, Gemini, OpenCode, OpenClaw).
Includes path traversal protection via canonicalize + starts_with validation,
session ID verification against file contents, frontend confirmation dialog
with optimistic cache updates, i18n keys (zh/en/ja), and component tests.
Jason