Add per-widget border option (style, thickness, palette color)

A Widget-level property (border_style/border_thickness/border_color_index),
not a per-type config field, since every widget type can have one -- drawn
once centrally in device.py's _render_widgets before compositing, using
an exact panel palette color so it never dithers. Styles: solid, dashed,
dotted, and a fancy double-line picture-frame-mat look. Configurable from
a shared "Border" card in every widget's gear-icon dialog.

server/app/image_pipeline.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import io
+import math
 
 from PIL import Image, ImageDraw, ImageEnhance, ImageFont, ImageOps
 
@@ -32,6 +33,83 @@ def draw_text(img: Image.Image, xy: tuple[int, int], text: str, font: ImageFont.
     mask = mask.point(lambda p: 255 if p > _TEXT_MASK_THRESHOLD else 0)
     img.paste(fill, (xy[0] + bbox[0], xy[1] + bbox[1]), mask)
 
+
+def _dashed_edge(draw: ImageDraw.ImageDraw, x0: float, y0: float, x1: float, y1: float,
+                 width: int, color: tuple[int, int, int], dash: float, gap: float) -> None:
+    length = math.hypot(x1 - x0, y1 - y0)
+    if length <= 0:
+        return
+    ux, uy = (x1 - x0) / length, (y1 - y0) / length
+    pos = 0.0
+    while pos < length:
+        end = min(pos + dash, length)
+        draw.line([(x0 + ux * pos, y0 + uy * pos), (x0 + ux * end, y0 + uy * end)], fill=color, width=width)
+        pos += dash + gap
+
+
+def _dotted_edge(draw: ImageDraw.ImageDraw, x0: float, y0: float, x1: float, y1: float,
+                 width: int, color: tuple[int, int, int], spacing: float) -> None:
+    length = math.hypot(x1 - x0, y1 - y0)
+    if length <= 0:
+        return
+    ux, uy = (x1 - x0) / length, (y1 - y0) / length
+    r = max(1, width / 2)
+    pos = 0.0
+    while pos <= length:
+        cx, cy = x0 + ux * pos, y0 + uy * pos
+        draw.ellipse([cx - r, cy - r, cx + r, cy + r], fill=color)
+        pos += spacing
+
+
+def draw_widget_border(img: Image.Image, style: str, thickness: int, color: tuple[int, int, int]) -> None:
+    """Draws a border inset within img's own bounds, mutating it in
+    place -- called once per widget's own region (routers/device.py's
+    _render_widgets, and each widget type's own dialog preview) before
+    that region's image is pasted onto the shared canvas, so a border
+    never straddles the boundary between two adjacent widgets. `color`
+    should already be an exact palette RGB (see resolve_border_color) so
+    the stroke quantizes with zero dithering error, same reasoning as
+    the weather/battery icons' exact-panel-ink-RGB fills.
+
+    "solid"/"dashed"/"dotted" are a single thickness-px stroke traced
+    just inside the image's edge; "fancy" is two thinner concentric
+    strokes with a gap between them, picture-frame-mat style. "none" (or
+    a non-positive thickness) draws nothing."""
+    if style == "none" or thickness <= 0:
+        return
+    w, h = img.size
+    t = max(1, min(int(thickness), min(w, h) // 2))
+    draw = ImageDraw.Draw(img)
+
+    if style == "fancy":
+        line_t = max(1, t // 3)
+        gap = max(2, t - 2 * line_t)
+        draw.rectangle([0, 0, w - 1, h - 1], outline=color, width=line_t)
+        inset = line_t + gap
+        if w - 2 * inset > 1 and h - 2 * inset > 1:
+            draw.rectangle([inset, inset, w - 1 - inset, h - 1 - inset], outline=color, width=line_t)
+        return
+
+    if style == "solid":
+        draw.rectangle([0, 0, w - 1, h - 1], outline=color, width=t)
+        return
+
+    # dashed/dotted trace the same centered-on-the-edge path solid/
+    # fancy's rectangle outline draws, so all four styles sit at the
+    # same inset regardless of which is chosen.
+    half = t / 2
+    x0, y0, x1, y1 = half, half, w - 1 - half, h - 1 - half
+    edges = [(x0, y0, x1, y0), (x1, y0, x1, y1), (x1, y1, x0, y1), (x0, y1, x0, y0)]
+    if style == "dashed":
+        dash, gap = t * 3, t * 2
+        for ex0, ey0, ex1, ey1 in edges:
+            _dashed_edge(draw, ex0, ey0, ex1, ey1, t, color, dash, gap)
+    elif style == "dotted":
+        spacing = max(t * 2, t + 4)
+        for ex0, ey0, ex1, ey1 in edges:
+            _dotted_edge(draw, ex0, ey0, ex1, ey1, t, color, spacing)
+
+
 # How each orientation maps the logically-composed image onto the native
 # 800x480 panel. "portrait"/"portrait_flipped" compose at 480x800 (so the
 # crop ratio matches how the frame actually hangs) and rotate into native
@@ -94,6 +172,21 @@ PALETTE_LABELS = ["Black", "White", "Yellow", "Red", "Blue", "Green"]
 # upstream.
 PANEL_CODES = [0x0, 0x1, 0x2, 0x3, 0x5, 0x6]
 
+# Per-widget optional border (models.Widget.border_style, see
+# draw_widget_border below). "none" is the default/no-op; the rest are
+# thickness-px strokes inset within the widget's own region.
+BORDER_STYLES = ["none", "solid", "dashed", "dotted", "fancy"]
+BORDER_STYLE_LABELS = {
+    "none": "None",
+    "solid": "Solid",
+    "dashed": "Dashed",
+    "dotted": "Dotted",
+    "fancy": "Fancy (double line)",
+}
+MIN_BORDER_THICKNESS = 1
+MAX_BORDER_THICKNESS = 8
+DEFAULT_BORDER_THICKNESS = 3
+
 
 def palette_to_hex(palette_rgb: list) -> list[str]:
     """[(0,0,0), ...] -> ["#000000", ...], for pre-filling the Advanced
@@ -101,6 +194,21 @@ def palette_to_hex(palette_rgb: list) -> list[str]:
     return ["#%02x%02x%02x" % tuple(c) for c in palette_rgb]
 
 
+def resolve_border_color(color_index: int, palette_rgb: list | None) -> tuple[int, int, int]:
+    """Widget.border_color_index -> an actual RGB tuple, against this
+    frame's tuned palette if it has one (falls back to
+    DEFAULT_PALETTE_RGB) -- so a border always renders as one of the
+    panel's real 6 ink colors and never needs to be dithered, same
+    reasoning as the weather/battery icons' exact-panel-ink-RGB fills
+    (see docs/widgets.md). Out-of-range indexes (a stale value from a
+    frame that used to have more colors, though that never happens
+    today) fall back to Black rather than raising."""
+    palette = palette_rgb or DEFAULT_PALETTE_RGB
+    if 0 <= color_index < len(palette):
+        return tuple(palette[color_index])
+    return tuple(palette[0])
+
+
 def hex_to_rgb(hex_str: str) -> tuple[int, int, int] | None:
     """"#1a2b3c" -> (26, 43, 60), or None for anything that isn't exactly
     a 6-hex-digit color (what <input type="color"> always sends, but a