Add agent components 451-465 and icon.Crystal

Fifteen components that dress an AI agent's work as an RPG party:
AgentCard, ToolCall, PlanQuest, ThinkingOrb, TokenMana, ApprovalPrompt,
AgentLog, SubAgentParty, MemoryCrystals, AgentStatus, DiffScroll,
ModelSelect, PromptBox, CostCoins and Checkpoints.

The context window is HP and the token budget MP; tool calls are spells
that CAST, glow, then land OK or FAILED; the transcript reads as a battle
log whose newest line types itself out; models line up like fighters.
Busy signs keep moving under Reduce Motion, decoration stops. Commands
and prompts never reach the log, and a veiled PromptBox casts nothing.

icon.Crystal is the new 12x12 save and memory crystal.

agent/agent.go

@@ -0,0 +1,72 @@
+// Package agent dresses AI agent work as an RPG party.
+package agent
+
+import (
+	"fmt"
+	"strconv"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/icon"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+// Status is where an agent stands.
+type Status int
+
+const (
+	Idle Status = iota
+	Working
+	Blocked
+	Done
+)
+
+// look is a status's word and slot; unknown ones panic.
+func (s Status) look(k pixel.Kit) (string, pixel.Slot) {
+	if s < Idle || s > Done {
+		panic(fmt.Sprintf("agent: unknown Status %d", s))
+	}
+	return k.Msg([...]string{"idle", "working", "blocked", "done"}[s]), [...]pixel.Slot{pixel.Faint, pixel.Info, pixel.Warn, pixel.Good}[s]
+}
+
+// tokens prints n short: 950, 1.5K, 128K, 2M.
+func tokens(n int) string {
+	if n < 1000 {
+		return strconv.Itoa(n)
+	}
+	div, unit := 1000, 0
+	for n/div >= 1000 {
+		div, unit = div*1000, unit+1
+	}
+	s := strconv.Itoa(n / div)
+	if t := n % div / (div / 10); n/div < 10 && t > 0 {
+		s += "." + strconv.Itoa(t)
+	}
+	return s + "KMBTPE"[unit:unit+1]
+}
+
+// gauge frames a bar eight dots high and fills part.
+func gauge(g pixel.Canvas, x, y, w int, part float64, ink pixel.Slot) {
+	g.Frame(x, y, w, 8, pixel.Sunken, pixel.Well)
+	g.Rect(x+2, y+2, int(part*float64(w-4)), 4, ink)
+}
+
+// health: Good past half, Warn past a quarter, else Bad.
+func health(left, full int) pixel.Slot {
+	switch {
+	case left <= full/4:
+		return pixel.Bad
+	case left <= full/2:
+		return pixel.Warn
+	}
+	return pixel.Good
+}
+
+// portrait is p or the robot; over 12 dots panics.
+func portrait(name string, p *pixel.Sprite) *pixel.Sprite {
+	if p == nil {
+		return icon.Robot
+	}
+	if p.W > 12 || p.H > 12 {
+		panic(fmt.Sprintf("agent: %s portrait is %dx%d, over 12", name, p.W, p.H))
+	}
+	return p
+}