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>

1 files changed, 11 insertions, 1 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.