feat: give the clock its own font

Installs Oswald (OFL-1.1, from googlefonts/OswaldFont) under
~/.fonts/o/Oswald with its license, and points the clock numerals at it
for the squared look the rounded Noto Sans Black did not have.

Per-widget fonts needed no new machinery: card.font() already takes any
family string, so FONT_* are shared defaults rather than a restriction.
FONT_CLOCK joins them, and the weather card keeps FONT_HEAVY, so the two
no longer have to agree.

Cairo still cannot ask for a weight above bold, so a heavier cut is
selected by family name as FONT_HEAVY already did. Worth knowing that
fontconfig substitutes a default for a family it does not recognise,
which is indistinguishable from the font not applying; fc-match tells
you which happened.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

3 files changed, 24 insertions, 2 deletions

diff --git a/README.md b/README.md
index d7cce00..9c4af64 100644
--- a/README.md
+++ b/README.md
@@ -206,7 +206,17 @@ to Lua either. What Lua does get is `conky_config`, the config file's path, so
 `dashboard.lua` opens that file and parses the hex out of it.
 
 **Cairo has no Black font weight.** `CAIRO_FONT_WEIGHT_BOLD` is the maximum, so
-the heavy clock numerals ask for the family `Noto Sans Black` at normal weight.
+a heavier cut is selected by the family name fontconfig registers for it, e.g.
+`Noto Sans Black` or `Oswald SemiBold` at normal weight, rather than by asking
+for bold.
+
+**Fonts are per-widget when a widget wants one.** `lib/card.lua` holds the
+shared `FONT_*` families, but `card.font()` takes any family string, so a
+widget passes its own. The clock uses `FONT_CLOCK` (Oswald, OFL-1.1, under
+`~/.fonts/o/Oswald`) for squared numerals while the weather card keeps
+`FONT_HEAVY`. Check a new family with `fc-match` first: fontconfig silently
+substitutes a default for a name it does not know, which looks exactly like the
+font "not applying".
 
 **Sensors are globbed by hwmon `name`, never by index.** Indices drift across
 kernel and hardware reorders, and a stale one silently reports a different chip.
diff --git a/lib/card.lua b/lib/card.lua
index 4d94465..3352c4b 100644
--- a/lib/card.lua
+++ b/lib/card.lua
@@ -13,6 +13,18 @@ M.FONT_MONO  = 'Inconsolata Nerd Font'
 M.FONT_UI    = 'Noto Sans'
 M.FONT_HEAVY = 'Noto Sans Black'
 
+-- Shared defaults, not a restriction: card.font() takes any family string, so
+-- a widget wanting its own face just passes one. The clock does, for squared
+-- numerals (Oswald, OFL-1.1, installed under ~/.fonts/o/Oswald).
+--
+-- Cairo can only ask for Regular or Bold by weight, so a heavier cut is
+-- selected by the family name fontconfig registers for it, exactly as
+-- FONT_HEAVY does above: 'Oswald SemiBold' at NORMAL weight, not 'Oswald' at
+-- bold. Fontconfig silently substitutes a default for a family it does not
+-- know, which looks identical to the font "not applying", so check a new name
+-- with `fc-match` before trusting it.
+M.FONT_CLOCK = 'Oswald'
+
 function M.font(cr, family, size, bold)
   cairo_select_font_face(cr, family, CAIRO_FONT_SLANT_NORMAL,
     bold and CAIRO_FONT_WEIGHT_BOLD or CAIRO_FONT_WEIGHT_NORMAL)
diff --git a/widgets/clock.lua b/widgets/clock.lua
index c3e9712..b7c80d9 100644
--- a/widgets/clock.lua
+++ b/widgets/clock.lua
@@ -33,7 +33,7 @@ function M.draw(cr, rect, colors)
   local avail = (bottom - date_band) - inner.y
   local size = math.min(avail * 0.46, inner.w * 0.95)
 
-  card.font(cr, card.FONT_HEAVY, size, false)
+  card.font(cr, card.FONT_CLOCK, size, true)
   card.rgba(cr, colors.body)
 
   -- Baselines. Cairo's y is the baseline, so the first sits one cap-height