feat(P01): orca init full bootstrap + schema 0006

orca init transforms from a bare mkdir into a full single-node cluster
bootstrap. After `orca init`, `orca doctor` passes with zero FAILs
on the bootstrap checks (CA, cert, db, localhost node).

Changes:
- migration 0006: nodes.kind + nodes.os nullable columns (REQ-049)
- model.Node: Kind + OS fields + NodeKind constants (localhost|linux|proxmox)
- NodeRepo: extended Insert/Get/List/Watch/scanNode for kind/os columns
  (NULL -> "" mapping); added GetByName + UpdateLastSeenAndOS helpers
- internal/cli/osdetect.go: detectOS() from /etc/os-release ID= field
  (D-032); fallback to /usr/lib/os-release then "linux"
- internal/cli/init.go: full bootstrap sequence (REQ-047, REQ-048):
  1. MkdirAll namespace dir
  2. store.Open (runs migrations 0001..0006)
  3. security.CAInit (idempotent fast-path)
  4. server cert gen if absent (D-036: skip if present)
  5. detectOS from /etc/os-release
  6. localhost node upsert (insert if new, refresh last_seen+os if exists)
  Idempotent re-run: no duplicate node, no cert regen, id/joined_at preserved
- --json output: full bootstrap summary (namespace, db, ca_fp, cert_fp,
  os, node_id, steps array)
- tests: init idempotency, osdetect parsing (ubuntu/debian/alpine/pve),
  kind/os round-trip, NULL->"" mapping, GetByName, UpdateLastSeenAndOS

E2E smoke test: orca init -> 5 PASS / 0 WARN / 1 FAIL (network=daemon
not running, expected); orca node list shows localhost node (os=ubuntu).

---ci---
project: orca
phase: 1
milestone: v0.6
status: execute
---/ci---

internal/model/node.go

@@ -10,6 +10,19 @@ const (
 	NodeStateLeft    NodeState = "left"
 )
 
+// NodeKind classifies a node by how it joined the cluster.
+type NodeKind string
+
+const (
+	// NodeKindLocalhost is the auto-registered local node from `orca init`.
+	NodeKindLocalhost NodeKind = "localhost"
+	// NodeKindLinux is a generic Linux node (ubuntu/debian/alpine) joined
+	// without a specific type. Reserved for future SSH-join flows.
+	NodeKindLinux NodeKind = "linux"
+	// NodeKindProxmox is a Proxmox VE 8/9 host joined via SSH bootstrap.
+	NodeKindProxmox NodeKind = "proxmox"
+)
+
 type Node struct {
 	ID       string            `json:"id"`
 	Name     string            `json:"name"`
@@ -18,4 +31,10 @@ type Node struct {
 	JoinedAt time.Time         `json:"joined_at"`
 	LastSeen time.Time         `json:"last_seen"`
 	Metadata map[string]string `json:"metadata,omitempty"`
+	// Kind classifies the node: localhost | linux | proxmox (REQ-049).
+	// Empty string for rows created before migration 0006.
+	Kind string `json:"kind,omitempty"`
+	// OS is the auto-detected OS identifier from /etc/os-release ID=
+	// (ubuntu|debian|alpine|pve|linux). Empty for pre-0006 rows.
+	OS string `json:"os,omitempty"`
 }