feat: 4-app signal composition demo with explicit outputs

Add 3 new streaming apps with explicit output declarations:
- streaming-clock.ds: output hours, minutes, seconds (tick private)
- streaming-stats.ds: output total, average, max (sum private)
- streaming-mood.ds: output mood, energy, color (clicks private)

Add compose-dashboard.ds that receives all 4 streams via unique
relay channels (/stream/default, /stream/clock, /stream/stats,
/stream/mood) into a single dashboard view.

Each app demonstrates selective signal registration — only declared
outputs are streamed, internal state remains private.

examples/compose-dashboard.ds

@@ -0,0 +1,53 @@
+-- DreamStack 4-App Composition Dashboard
+-- Composes signals from 4 independent streaming apps.
+-- Each app has explicit output declarations:
+--   counter: count, doubled   (NOT message)
+--   clock:   hours, minutes, seconds (NOT tick)
+--   stats:   total, average, max (NOT sum, last_sample)
+--   mood:    mood, energy, color (NOT clicks)
+--
+-- Run with:
+--   Tab 1: cargo run -p ds-stream
+--   Tab 2: dreamstack stream examples/streaming-counter.ds --port 3000
+--   Tab 3: dreamstack stream examples/streaming-clock.ds --port 3002
+--   Tab 4: dreamstack stream examples/streaming-stats.ds --port 3003
+--   Tab 5: dreamstack stream examples/streaming-mood.ds --port 3004
+--   Tab 6: dreamstack build examples/compose-dashboard.ds
+--
+--   Open the built file in a browser.
+
+let counter = stream from "ws://localhost:9100/stream/default"
+let clock = stream from "ws://localhost:9100/stream/clock"
+let stats = stream from "ws://localhost:9100/stream/stats"
+let mood = stream from "ws://localhost:9100/stream/mood"
+
+view main =
+  column [
+    text "🎛️ DreamStack Signal Composition"
+    text "4 apps → 1 dashboard"
+    row [
+      column [
+        text "── 🔢 Counter ──"
+        text "Count: {counter.count}"
+        text "Doubled: {counter.doubled}"
+      ]
+      column [
+        text "── 🕐 Clock ──"
+        text "{clock.hours}:{clock.minutes}:{clock.seconds}"
+      ]
+    ]
+    row [
+      column [
+        text "── 📊 Stats ──"
+        text "Samples: {stats.total}"
+        text "Average: {stats.average}"
+        text "Max: {stats.max}"
+      ]
+      column [
+        text "── 😊 Mood ──"
+        text "Mood: {mood.mood}"
+        text "Energy: {mood.energy}%"
+        text "Color: {mood.color}"
+      ]
+    ]
+  ]

examples/streaming-clock.ds

@@ -0,0 +1,25 @@
+-- DreamStack Streaming Clock
+-- Streams time signals every second.
+-- Only hours, minutes, seconds are exposed (tick is internal).
+--
+-- Run with:
+--   dreamstack stream examples/streaming-clock.ds --port 3002
+
+let tick = 0
+let seconds = tick % 60
+let minutes = (tick / 60) % 60
+let hours = (tick / 3600) % 24
+
+stream clock on "ws://localhost:9100/peer/clock" {
+  mode: signal,
+  output: hours, minutes, seconds
+}
+
+every 1000 -> tick += 1
+
+view clock =
+  column [
+    text "🕐 Streaming Clock"
+    text "{hours}:{minutes}:{seconds}"
+    text "tick: {tick}"
+  ]

examples/streaming-mood.ds

@@ -0,0 +1,50 @@
+-- DreamStack Streaming Mood
+-- Interactive mood and energy tracker.
+-- Only mood, energy, color are exposed (clicks is internal).
+--
+-- Run with:
+--   dreamstack stream examples/streaming-mood.ds --port 3004 --relay ws://localhost:9100/source/mood
+
+let mood = "neutral"
+let energy = 50
+let color = "gray"
+let clicks = 0
+
+stream mood_tracker on "ws://localhost:9100/peer/mood" {
+  mode: signal,
+  output: mood, energy, color
+}
+
+view mood_tracker =
+  column [
+    text "😊 Mood Tracker"
+    text "Mood: {mood}"
+    text "Energy: {energy}%"
+    text "Color: {color}"
+    row [
+      button "😄 Happy" {
+        click: mood = "happy"
+        click: color = "green"
+        click: energy = energy + 10
+      }
+      button "😐 Neutral" {
+        click: mood = "neutral"
+        click: color = "gray"
+      }
+      button "😤 Angry" {
+        click: mood = "angry"
+        click: color = "red"
+        click: energy = energy - 10
+      }
+    ]
+    row [
+      button "☕ Caffeine" {
+        click: energy = energy + 25
+        click: clicks += 1
+      }
+      button "😴 Rest" {
+        click: energy = energy - 15
+        click: clicks += 1
+      }
+    ]
+  ]

examples/streaming-stats.ds

@@ -0,0 +1,44 @@
+-- DreamStack Streaming Stats
+-- Tracks button presses and computes statistics.
+-- Only total, average, max are exposed (sum and last_sample are internal).
+--
+-- Run with:
+--   dreamstack stream examples/streaming-stats.ds --port 3003
+
+let total = 0
+let max = 0
+let sum = 0
+let average = sum / (total + 1)
+
+stream stats on "ws://localhost:9100/peer/stats" {
+  mode: signal,
+  output: total, average, max
+}
+
+view stats =
+  column [
+    text "📊 Streaming Stats"
+    text "Samples: {total}"
+    text "Average: {average}"
+    text "Max: {max}"
+    row [
+      button "+5" {
+        click: total += 1
+        click: sum += 5
+      }
+      button "+10" {
+        click: total += 1
+        click: sum += 10
+      }
+      button "+25" {
+        click: total += 1
+        click: sum += 25
+        click: max = 25
+      }
+      button "+50" {
+        click: total += 1
+        click: sum += 50
+        click: max = 50
+      }
+    ]
+  ]