feat(plugin): add /claude-mailbox:mailbox-doctor for one-command setup

The doctor command runs entirely inside Claude Code and walks through:
binary install via npm, daemon autostart, mailbox-name prompt with write
to per-project `.claude/settings.json` env, and a self → self smoke test.
Also adds `/claude-mailbox:mailbox-status` as a read-only health check.

Reduces the colleague onboarding to: add marketplace, install plugin,
run the doctor — no terminal context-switch required.

plugin/commands/mailbox-doctor.md

@@ -0,0 +1,85 @@
+---
+description: Diagnose and auto-fix the Claude-Mailbox setup (binary install, daemon autostart, mailbox name, smoke test).
+allowed-tools: Bash, Read, Edit, Write
+---
+
+You are running the **Claude-Mailbox doctor**. Walk through these checks in order. After each check, print a one-line status (✓ / ✗) and the action you took. At the very end, print a final summary block.
+
+Throughout, prefer the dedicated tools (`Read`, `Edit`, `Write`) for files. Use `Bash` only for `claude-mailbox` subcommands, `npm`, `where`/`which`, and `cat /etc/os-release` style lookups. Never run `sudo` automatically — if elevation is needed, stop and ask the user how to proceed.
+
+---
+
+## Step 1 — daemon binary on PATH
+
+Run: `claude-mailbox --version`
+
+- **Exit 0** → binary present. Record the version string. ✓ continue.
+- **Command not found / non-zero exit** → binary missing. Tell the user the install command for their platform and ask before running it:
+
+  | Platform | Install command |
+  |---|---|
+  | Windows | `npm install -g @kuns/claude-mailbox` (no admin) |
+  | macOS / Linux | `npm install -g @kuns/claude-mailbox` (may need `sudo` depending on Node setup; ask the user if `npm install` fails with EACCES) |
+
+  Prerequisite: `npm config get @kuns:registry` should return `https://git.kuns.dev/api/packages/releases/npm/`. If it doesn't, set it first:
+
+  ```
+  npm config set @kuns:registry=https://git.kuns.dev/api/packages/releases/npm/
+  ```
+
+  After install, re-run `claude-mailbox --version`. If it still fails, stop and report the error.
+
+## Step 2 — daemon autostart and running state
+
+Run: `claude-mailbox status`
+
+- **`Running`** → ✓ continue.
+- **`Stopped`** → run `claude-mailbox start`. Re-check status.
+- **`NotInstalled`** → run `claude-mailbox install-autostart`, then `claude-mailbox start`. Re-check status.
+
+If status doesn't become `Running` after the fix, stop and report what `status` and `start` printed.
+
+Sanity check: `curl -sf http://127.0.0.1:47822/health` (or use Bash to fetch it). Expect a JSON body with `"status":"ok"`.
+
+## Step 3 — mailbox name in project settings
+
+The hook reads the mailbox name from `$CLAUDE_MAILBOX_NAME`. Claude Code injects env vars from `.claude/settings.json` into hook commands, so the cleanest place to set it is per-project.
+
+1. Read `.claude/settings.json` in the current working directory (it may not exist yet — that's fine).
+2. Check if `env.CLAUDE_MAILBOX_NAME` is set.
+3. If **set**: ✓ continue, record the name.
+4. If **not set**:
+   - Ask the user for a mailbox name. Suggest a default based on the cwd basename (e.g., for `C:\Private\Claude-Mailbox` suggest `claude-mailbox`). Names should be short, kebab-case-ish, unique among parallel Claude sessions.
+   - Read existing `.claude/settings.json` if present, otherwise start with `{}`.
+   - Set/merge `env.CLAUDE_MAILBOX_NAME` to the chosen name. Preserve any other existing settings.
+   - Write back with 2-space indentation.
+   - Tell the user they need to **restart this Claude Code session** for the env to take effect in the hook — but the smoke test below can still run because we'll pass `--name` explicitly.
+
+## Step 4 — smoke test
+
+Use the resolved name from step 3 (either pre-existing or just chosen). Run:
+
+```
+claude-mailbox send  --from doctor-probe --to <name> --body "ping from /claude-mailbox:mailbox-doctor"
+claude-mailbox check --name <name>
+```
+
+- The `check` output should be a JSON array containing exactly one message with `"from": "doctor-probe"` and that body.
+- If yes: ✓ smoke test passed.
+- If no (empty array, error, or wrong message): ✗ report what was returned.
+
+## Step 5 — final summary
+
+Print a compact block with these fields, one per line:
+
+```
+Claude-Mailbox doctor
+  binary:       <version>
+  daemon:       Running | Stopped | NotInstalled  (and what you did)
+  health:       ok | unreachable
+  mailbox name: <name>  (source: existing | newly written to .claude/settings.json)
+  smoke test:   passed | failed
+  restart hint: <yes if name was newly written, otherwise no>
+```
+
+If everything is ✓ and `restart hint: yes`, end with: "Restart Claude Code (or open a new session) so the UserPromptSubmit hook picks up `CLAUDE_MAILBOX_NAME`." If `restart hint: no`, end with: "You're good to go — unread messages will appear before your next prompt."

plugin/commands/mailbox-status.md

@@ -0,0 +1,23 @@
+---
+description: Read-only Claude-Mailbox health check. No changes, no installs — just report.
+allowed-tools: Bash, Read
+---
+
+Report the Claude-Mailbox setup status without making any changes. If something is wrong, **tell** the user but **do not** fix it — suggest `/claude-mailbox:mailbox-doctor` for that.
+
+Print exactly this block, filling in each line:
+
+```
+Claude-Mailbox status
+  binary:       <output of `claude-mailbox --version`, or "not installed">
+  daemon:       <output of `claude-mailbox status`>
+  health:       <"ok" if GET http://127.0.0.1:47822/health returns 200, else "unreachable">
+  mailbox name: <value of env.CLAUDE_MAILBOX_NAME in ./.claude/settings.json, or "unset"; also note if ~/.claude/settings.json has a value>
+  pending:      <integer count from `claude-mailbox peek --name <resolved-name>` if name is set, else "n/a">
+```
+
+End with one line:
+
+- All good → `Status: OK`
+- Missing daemon or unset name → `Status: Setup incomplete. Run /claude-mailbox:mailbox-doctor to fix.`
+- Daemon installed but stopped → `Status: Daemon is not running. Try \`claude-mailbox start\` or run /claude-mailbox:mailbox-doctor.`