docs: add group deployment support to homelab-deploy plan

Support deploying to all hosts in a tier or all hosts with a role:
- deploy.<tier>.all - broadcast to all hosts in tier
- deploy.<tier>.role.<role> - broadcast to hosts with matching role

MCP can deploy to all test hosts at once, admin can deploy to any group.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/plans/nats-deploy-service.md

@@ -74,8 +74,10 @@ homelab-deploy listener --hostname ns1 --nats-url nats://nats1:4222
 homelab-deploy mcp --nats-url nats://nats1:4222
 
 # CLI commands for manual use
-homelab-deploy deploy ns1 --branch feature-x --action switch
-homelab-deploy deploy --all --action boot
+homelab-deploy deploy ns1 --branch feature-x --action switch  # single host
+homelab-deploy deploy --tier test --all --action boot          # all test hosts
+homelab-deploy deploy --tier prod --all --action boot          # all prod hosts (admin only)
+homelab-deploy deploy --tier prod --role dns --action switch   # all prod dns hosts
 homelab-deploy status
 ```
 
@@ -84,11 +86,28 @@ homelab-deploy status
 ### Listener Mode
 
 A systemd service on each host that:
-- Subscribes to `deploy.<tier>.<hostname>` and `deploy.<tier>.all` subjects
+- Subscribes to multiple subjects for targeted and group deployments
 - Validates incoming messages (revision, action)
 - Executes `nixos-rebuild` with specified parameters
 - Reports status back via NATS
 
+**Subject structure:**
+```
+deploy.<tier>.<hostname>      # specific host (e.g., deploy.prod.ns1)
+deploy.<tier>.all             # all hosts in tier (e.g., deploy.test.all)
+deploy.<tier>.role.<role>     # all hosts with role in tier (e.g., deploy.prod.role.dns)
+```
+
+**Listener subscriptions** (based on `homelab.host` config):
+- `deploy.<tier>.<hostname>` - direct messages to this host
+- `deploy.<tier>.all` - broadcast to all hosts in tier
+- `deploy.<tier>.role.<role>` - broadcast to hosts with matching role (if role is set)
+
+Example: ns1 with `tier=prod, role=dns` subscribes to:
+- `deploy.prod.ns1`
+- `deploy.prod.all`
+- `deploy.prod.role.dns`
+
 **NixOS module configuration:**
 ```nix
 services.homelab-deploy.listener = {
@@ -97,7 +116,7 @@ services.homelab-deploy.listener = {
 };
 ```
 
-The listener reads its tier from `config.homelab.host.tier` (see Host Metadata below) and subscribes to tier-specific subjects (e.g., `deploy.prod.ns1` and `deploy.prod.all`).
+The listener reads tier and role from `config.homelab.host` (see Host Metadata below).
 
 **Request message format:**
 ```json
@@ -133,11 +152,16 @@ This provides immediate feedback on validation errors (bad revision, already run
 ### MCP Mode
 
 Runs as an MCP server providing tools for Claude Code:
-- `deploy` - Deploy to specific host(s) with optional revision
+- `deploy` - Deploy to specific host, all hosts in tier, or all hosts with a role
 - `deploy_status` - Check deployment status/history
 - `list_hosts` - List available deployment targets
 
-The MCP server runs with limited credentials (test-tier only), so Claude can deploy to test hosts but not production.
+The MCP server runs with limited credentials (test-tier only), so Claude can:
+- Deploy to individual test hosts
+- Deploy to all test hosts at once (`deploy.test.all`)
+- Deploy to test hosts by role (`deploy.test.role.<role>`)
+
+Production deployments require admin credentials.
 
 ### Tiered Permissions
 
@@ -183,11 +207,15 @@ accounts = {
 | test | template1, nix-cache01, future test hosts |
 | prod | ns1, ns2, ha1, monitoring01, http-proxy, etc. |
 
-**How it works:**
-1. MCP tries to deploy to ns1 → publishes to `deploy.prod.ns1`
-2. NATS server rejects publish (mcp-deployer lacks `deploy.prod.>` permission)
-3. MCP tries to deploy to template1 → publishes to `deploy.test.template1`
-4. NATS allows it, listener receives and executes
+**Example deployment scenarios:**
+
+| Command | Subject | MCP | Admin |
+|---------|---------|-----|-------|
+| Deploy to ns1 | `deploy.prod.ns1` | ❌ | ✅ |
+| Deploy to template1 | `deploy.test.template1` | ✅ | ✅ |
+| Deploy to all test hosts | `deploy.test.all` | ✅ | ✅ |
+| Deploy to all prod hosts | `deploy.prod.all` | ❌ | ✅ |
+| Deploy to all DNS servers | `deploy.prod.role.dns` | ❌ | ✅ |
 
 All NKeys stored in Vault - MCP gets limited credentials, admin CLI gets full-access credentials.