feat: stdio MCP wrapper + Windows Run-key autostart fallback (v1.0.1)

Two production-readiness fixes so colleagues can install cleanly:

1. Plugin's MCP server now spawns `claude-mailbox mcp-stdio`, a small
   stdio MCP wrapper that proxies tool calls to the daemon's REST API.
   Claude Code does not support env-var substitution in HTTP MCP `url`
   fields (issue #46889), so the wrapper is the only way to make the
   daemon URL configurable per machine via CLAUDE_MAILBOX_URL.

2. Windows `install-autostart` now falls back from `schtasks /Create`
   to an HKCU\Software\Microsoft\Windows\CurrentVersion\Run entry
   when Group Policy blocks the Scheduled Task path. Both modes are
   per-user, no admin, persist across logoffs. The chosen mode is
   recorded in ~/.claude-mailbox/autostart-mode so status/start/stop/
   uninstall-autostart pick the right cleanup path.

Also bumps the npm version to 1.0.1 to align with the published 1.0.0
plus this patch.

plugin/.mcp.json

@@ -1,8 +1,9 @@
 {
   "mcpServers": {
     "mailbox": {
-      "type": "http",
-      "url": "http://127.0.0.1:47822/mcp"
+      "type": "stdio",
+      "command": "claude-mailbox",
+      "args": ["mcp-stdio"]
     }
   }
 }

plugin/README.md

@@ -44,7 +44,9 @@ Cost: one local HTTP round-trip per prompt + Node coldstart (~100ms on Windows).
 
 ## MCP tools
 
-The plugin also ships a `.mcp.json` so Claude has direct access to the mailbox via tool calls. Because the X-Mailbox header would be the same for two parallel sessions sharing one `.mcp.json`, **each MCP tool takes the caller's mailbox name as an explicit argument** (from the SessionStart announcement):
+The plugin ships a `.mcp.json` that spawns a **stdio MCP wrapper** (`claude-mailbox mcp-stdio`) so the daemon URL is configurable per machine via the `CLAUDE_MAILBOX_URL` env var (Claude Code doesn't yet support env substitution in HTTP MCP URLs — see issue #46889). The wrapper proxies tool calls to the daemon's REST API.
+
+Each MCP tool takes the caller's mailbox name as an explicit argument (from the SessionStart announcement):
 
 | Tool | Required args | Purpose |
 |---|---|---|

plugin/commands/mailbox-doctor.md

@@ -59,11 +59,9 @@ Run: `claude-mailbox status`
 - `Stopped` → `claude-mailbox start`, re-check.
 - `NotInstalled` → `claude-mailbox install-autostart`, then `claude-mailbox start`, re-check.
 
-**If `install-autostart` fails with "Access is denied" on Windows:** Group Policy may block non-admin `schtasks /Create`. Two fallbacks:
-1. Tell the user to run `claude-mailbox install-autostart` from an elevated PowerShell themselves (one-time).
-2. For this session, run `claude-mailbox serve` as a background process so the rest of the doctor's checks can pass — the daemon won't survive logoff, but that's fine for verification.
+**Behavior on `install-autostart`:** The CLI tries a Scheduled Task first (`schtasks /RL LIMITED`, no admin). If Windows Group Policy returns "Access is denied", it falls back transparently to an `HKCU\Software\Microsoft\Windows\CurrentVersion\Run` registry entry plus a hidden `node serve` process — same per-user persistence, no admin needed. The chosen mechanism is recorded in `~/.claude-mailbox/autostart-mode` and respected by `status`/`start`/`stop`/`uninstall-autostart`.
 
-If status doesn't reach `Running` after the fallback, stop and report.
+If `install-autostart` still fails after both attempts (very rare — would mean both `schtasks` and `reg add` are blocked), stop and report what `status` and `start` printed.
 
 ## Step 4 — health probe