feat: add AppState enum and programmatic tray icon generation

Implements Task 5 of the TDD plan: creates the tray package with
AppState enum (WAITING, RECORDING, TRANSCRIBING) and a create_icon()
function that generates colorized microphone icons via Pillow.

- whisper_local/tray/__init__.py: empty package marker
- whisper_local/tray/_tray.py: AppState enum
- whisper_local/tray/_icon.py: icon generation with state-specific colors
- tests/test_tray.py: comprehensive test coverage for icon creation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

whisper_local/tray/__init__.py

@@ -0,0 +1 @@
+"""Tray-Package — wird in späteren Tasks befüllt."""

whisper_local/tray/_icon.py

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+"""Programmatische Icon-Generierung via Pillow."""
+
+from PIL import Image, ImageDraw
+
+from whisper_local.tray._tray import AppState
+
+_STATE_COLORS: dict[AppState, tuple[int, int, int]] = {
+    AppState.WAITING: (150, 150, 150),
+    AppState.RECORDING: (220, 50, 50),
+    AppState.TRANSCRIBING: (220, 180, 0),
+}
+
+
+def create_icon(state: AppState, size: int = 64) -> Image.Image:
+    """Erzeugt ein Mikrofon-Icon in der Farbe des übergebenen Zustands."""
+    color = _STATE_COLORS[state]
+    img = Image.new("RGBA", (size, size), (0, 0, 0, 0))
+    draw = ImageDraw.Draw(img)
+
+    cx = size // 2
+    bw = max(4, size // 6)   # Hälfte der Körperbreite
+    top = size // 8
+    mid = size // 2
+
+    # Mikrofon-Körper (abgerundetes Rechteck)
+    draw.rounded_rectangle(
+        [cx - bw, top, cx + bw, mid + bw],
+        radius=bw,
+        fill=color,
+    )
+
+    # Bogen (Stativ-Bogen)
+    arc_r = size // 4
+    arc_top = mid
+    lw = max(2, size // 20)
+    draw.arc(
+        [cx - arc_r, arc_top, cx + arc_r, arc_top + arc_r],
+        start=0, end=180, fill=color, width=lw,
+    )
+
+    # Stiel
+    pole_top = arc_top + arc_r // 2
+    pole_bot = size - size // 8
+    draw.line([cx, pole_top, cx, pole_bot], fill=color, width=lw)
+
+    # Sockel
+    base = size // 5
+    draw.line([cx - base, pole_bot, cx + base, pole_bot], fill=color, width=lw)
+
+    return img

whisper_local/tray/_tray.py

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+"""Tray-App und App-Zustände für whisper-local (Windows)."""
+
+import enum
+
+
+class AppState(enum.Enum):
+    WAITING = "waiting"
+    RECORDING = "recording"
+    TRANSCRIBING = "transcribing"