feat: add card-renderer internal service (v1)

- New card-renderer FastAPI service (Python 3.11 + Pillow)
  - GET /health, GET /templates
  - POST /render (URL input)
  - POST /render/file (multipart upload)
  - POST /render/meta (dry-run layout metadata)
  - nova-artwork-v1 template: cover crop, gradient overlay, text, logo
  - SSRF-safe async image fetch with redirect validation
  - Smart center cover crop isolated for future YOLO focal-point support
  - Graceful font/logo fallback when assets are absent

- docker-compose.yml: add card-renderer service + healthcheck;
  extend gateway with CARD_RENDERER_URL and depends_on

- gateway/main.py: proxy endpoints under /cards/*
  - GET  /cards/templates
  - POST /cards/render
  - POST /cards/render/file
  - POST /cards/render/meta
  All protected by existing APIKeyMiddleware

card-renderer/app/render.py

@@ -0,0 +1,113 @@
+from __future__ import annotations
+
+import os
+from pathlib import Path
+from typing import Optional
+
+from PIL import Image, ImageDraw, ImageFont
+
+from app.crop import smart_cover_crop
+
+# Asset paths — configurable via env so they can be overridden in compose.
+ASSETS = Path(os.getenv("CARD_ASSETS_DIR", "/app/assets"))
+FONT_REGULAR = os.getenv("CARD_DEFAULT_FONT", str(ASSETS / "fonts" / "Inter-Regular.ttf"))
+FONT_BOLD = os.getenv("CARD_BOLD_FONT", str(ASSETS / "fonts" / "Inter-Bold.ttf"))
+LOGO_PATH = os.getenv("CARD_LOGO_PATH", str(ASSETS / "logo.png"))
+
+
+def _load_font(path: str, size: int) -> ImageFont.FreeTypeFont | ImageFont.ImageFont:
+    """Load a TrueType font, falling back to PIL default if the file is absent."""
+    try:
+        return ImageFont.truetype(path, size=size)
+    except (OSError, IOError):
+        return ImageFont.load_default()
+
+
+def _truncate_text(text: str, max_chars: int) -> str:
+    """Truncate text with an ellipsis if it exceeds max_chars."""
+    if len(text) <= max_chars:
+        return text
+    return text[: max_chars - 1] + "\u2026"
+
+
+def _draw_gradient_overlay(base: Image.Image) -> None:
+    """Paint a bottom-weighted dark gradient over base (mutates in-place)."""
+    w, h = base.size
+    overlay = Image.new("RGBA", (w, h), (0, 0, 0, 0))
+    draw = ImageDraw.Draw(overlay)
+    for y in range(h):
+        # alpha ramps from 0 at top to ~200 at bottom
+        alpha = int(200 * (y / h) ** 1.5)
+        draw.line((0, y, w, y), fill=(0, 0, 0, alpha))
+    base.alpha_composite(overlay)
+
+
+def render_nova_artwork_v1(
+    source: Image.Image,
+    width: int,
+    height: int,
+    title: Optional[str],
+    subtitle: Optional[str],
+    username: Optional[str],
+    category: Optional[str],
+    show_logo: bool,
+) -> tuple[Image.Image, tuple[int, int, int, int]]:
+    """Render the nova-artwork-v1 card template.
+
+    Returns (rendered_image_RGBA, crop_box).
+    """
+    canvas, crop_box = smart_cover_crop(source, width, height)
+    canvas = canvas.convert("RGBA")
+
+    _draw_gradient_overlay(canvas)
+    draw = ImageDraw.Draw(canvas)
+
+    pad_x = 48
+    bottom = height - 48
+
+    title_font = _load_font(FONT_BOLD, 54)
+    meta_font = _load_font(FONT_REGULAR, 28)
+    small_font = _load_font(FONT_REGULAR, 22)
+
+    if category:
+        draw.text(
+            (pad_x, bottom - 156),
+            _truncate_text(category.upper(), 40),
+            font=small_font,
+            fill=(220, 220, 220, 235),
+        )
+
+    if title:
+        draw.text(
+            (pad_x, bottom - 116),
+            _truncate_text(title, 60),
+            font=title_font,
+            fill=(255, 255, 255, 255),
+        )
+
+    meta_parts = [p for p in [subtitle, username] if p]
+    if meta_parts:
+        draw.text(
+            (pad_x, bottom - 44),
+            " \u2022 ".join(_truncate_text(p, 40) for p in meta_parts),
+            font=meta_font,
+            fill=(235, 235, 235, 245),
+        )
+
+    if show_logo:
+        _composite_logo(canvas, width)
+
+    return canvas, crop_box
+
+
+def _composite_logo(canvas: Image.Image, canvas_width: int) -> None:
+    """Overlay the logo image in the top-right corner. Fails silently if absent."""
+    try:
+        logo = Image.open(LOGO_PATH).convert("RGBA")
+        logo.thumbnail((160, 60), Image.LANCZOS)
+        x = canvas_width - logo.width - 40
+        y = 36
+        canvas.alpha_composite(logo, (x, y))
+    except Exception:
+        # Logo is optional — missing or unreadable file is not an error
+        pass