feat(subagents): propagate approval mode to sub-agents (#3066)

* feat(subagents): propagate approval mode to sub-agents

Replace hardcoded PermissionMode.Default with resolution logic:
- Permissive parent modes (yolo, auto-edit) always win
- Plan-mode parents keep sub-agents in plan mode
- Agent definitions can declare approvalMode in frontmatter
- Default fallback is auto-edit in trusted folders
- Untrusted folders block privileged mode escalation

Also maps Claude permission aliases (acceptEdits, bypassPermissions,
dontAsk) to qwen-code approval modes in the converter.

* fix(subagents): correct dontAsk mapping and add approval mode resolution tests

Map Claude's `dontAsk` to `default` instead of `auto-edit` — `dontAsk`
denies prompts (restrictive) so `default` is a closer semantic match.

Add 9 unit tests covering the full `resolveSubagentApprovalMode` decision
matrix: permissive parent override, agent-declared modes, trusted/untrusted
folder blocking, and plan-mode fallback.

* test: remove flaky InputPrompt tab-suggestion test on Windows