feat: auto-avatar con proveedores gratuitos (DiceBear, RoboHash, Multiavatar)

Nuevo sistema de generacion automatica de avatares:

- pkg/avatar/ — tipos puros y URL builders para proveedores gratuitos:
  DiceBear (bottts, pixel-art, etc.), RoboHash (robots, monsters),
  Multiavatar (multicultural). Sin I/O.
- shell/avatar/ — fetcher impuro: descarga imagen por HTTP a temp file.
- agentctl auto-avatar <id> — genera, descarga, sube y activa avatar
  con un solo comando. Soporta --provider, --style, --set, --dry-run.

Respeta pure core / impure shell. El seed del avatar es el agent ID,
asi cada bot obtiene una imagen unica y determinista.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pkg/avatar/provider.go

@@ -0,0 +1,109 @@
+// Package avatar provides pure types and URL builders for avatar image providers.
+// No I/O — only data transformations.
+package avatar
+
+import (
+	"fmt"
+	"net/url"
+)
+
+// Provider identifies an avatar generation service.
+type Provider string
+
+const (
+	// ProviderDiceBear generates illustrated avatars via DiceBear API.
+	// Styles: adventurer, avataaars, bottts, fun-emoji, identicon, initials,
+	// lorelei, micah, miniavs, notionists, open-peeps, personas, pixel-art, shapes, thumbs.
+	ProviderDiceBear Provider = "dicebear"
+
+	// ProviderRoboHash generates robot/monster/head images from any text.
+	// Sets: set1 (robots), set2 (monsters), set3 (heads), set4 (cats), set5 (humans).
+	ProviderRoboHash Provider = "robohash"
+
+	// ProviderMultiavatar generates unique multicultural avatars from a string.
+	ProviderMultiavatar Provider = "multiavatar"
+)
+
+// DiceBearStyle is a style option for the DiceBear provider.
+type DiceBearStyle string
+
+const (
+	DiceBearBottts    DiceBearStyle = "bottts"
+	DiceBearPixelArt  DiceBearStyle = "pixel-art"
+	DiceBearAdventurer DiceBearStyle = "adventurer"
+	DiceBearShapes    DiceBearStyle = "shapes"
+	DiceBearFunEmoji  DiceBearStyle = "fun-emoji"
+	DiceBearIdenticon DiceBearStyle = "identicon"
+	DiceBearThumbs    DiceBearStyle = "thumbs"
+)
+
+// RoboHashSet is a set option for the RoboHash provider.
+type RoboHashSet string
+
+const (
+	RoboHashRobots   RoboHashSet = "set1"
+	RoboHashMonsters RoboHashSet = "set2"
+	RoboHashHeads    RoboHashSet = "set3"
+	RoboHashCats     RoboHashSet = "set4"
+	RoboHashHumans   RoboHashSet = "set5"
+)
+
+// Options configures avatar generation.
+type Options struct {
+	// Size in pixels (square). Default: 256.
+	Size int
+
+	// DiceBear-specific style. Default: bottts.
+	DiceBearStyle DiceBearStyle
+
+	// RoboHash-specific set. Default: set1 (robots).
+	RoboHashSet RoboHashSet
+}
+
+// DefaultOptions returns sensible defaults for bot avatars.
+func DefaultOptions() Options {
+	return Options{
+		Size:          256,
+		DiceBearStyle: DiceBearBottts,
+		RoboHashSet:   RoboHashRobots,
+	}
+}
+
+// URL returns the avatar image URL for the given provider and seed (typically the agent name/ID).
+// Pure function — no I/O.
+func URL(provider Provider, seed string, opts Options) string {
+	if opts.Size <= 0 {
+		opts.Size = 256
+	}
+	encoded := url.PathEscape(seed)
+
+	switch provider {
+	case ProviderDiceBear:
+		style := opts.DiceBearStyle
+		if style == "" {
+			style = DiceBearBottts
+		}
+		return fmt.Sprintf("https://api.dicebear.com/9.x/%s/png?seed=%s&size=%d",
+			style, url.QueryEscape(seed), opts.Size)
+
+	case ProviderRoboHash:
+		set := opts.RoboHashSet
+		if set == "" {
+			set = RoboHashRobots
+		}
+		return fmt.Sprintf("https://robohash.org/%s.png?set=%s&size=%dx%d",
+			encoded, set, opts.Size, opts.Size)
+
+	case ProviderMultiavatar:
+		return fmt.Sprintf("https://api.multiavatar.com/%s.png?apikey=Wookie",
+			encoded)
+
+	default:
+		return URL(ProviderDiceBear, seed, opts)
+	}
+}
+
+// AllProviders returns the list of supported providers.
+func AllProviders() []Provider {
+	return []Provider{ProviderDiceBear, ProviderRoboHash, ProviderMultiavatar}
+}