fix(configure): stop misrouting Desktop users to the Code connector-verify path

[hyoshi]

Problem

A Claude Desktop user who had connected the Meta hosted MCP got the misleading "まだ接続されていません…(redo the Meta login)" when clicking finalize in mureo configure.

Root cause: the in-memory session.host can reset to the claude-code default (configure process restart; /api/host was posted only on radio change, fire-and-forget, errors swallowed). So confirm_hosted_provider ran the Claude Code claude mcp list verification path for a Desktop user; with no Claude Code CLI, is_hosted_provider_connected returned a bare False → mapped to not_connected, an accusatory dead-end. The official Meta MCP itself was always usable — only the switch-native-off step was wrongly blocked (tool ambiguity, never a strand).

Fix (scope 1+2+3)

1. Client-authoritative host — /api/providers/confirm and /api/providers/native-toggle resolve host from the request payload via _resolve_host (validated against SUPPORTED_HOSTS, written back to self-heal a stale session); finalize sends state.host.
2. Host-sync hardening (wizard.js) — persist the explicit choice to localStorage and prefer it over the server-echoed status.host; syncHostToServer retries once and shows a toast instead of swallowing failures; assert host on host-step entry and on onReady.
3. Tri-state connectivity — hosted_provider_connectivity → connected|not_connected|unknown. unknown (no Claude Code CLI / timeout / rc≠0) is not "not connected". is_hosted_provider_connected kept as a == "connected" wrapper (existing no-strand guards unchanged). confirm_hosted_provider gains affirm: Desktop / unknown no longer dead-end — an explicit user affirmation applies the switch (no-strand by deliberate consent). New EN/JA i18n + affirm button.

Tests

• New tri-state TestHostedProviderConnectivity; rewritten/extended confirm tests (unverifiable, affirm, Desktop+affirm); handler host-resolution tests; i18n EN/JA parity for new keys.
• Clean-env full suite: 3254 passed. ruff/black/mypy clean (changed files). JS syntax OK. code-reviewer: APPROVE (no CRITICAL/HIGH).

Out of scope (acknowledged, left as-is by maintainer): the separate setup_state.json ledger-vs-reality gap for upgraders.