fix(card): productive titles render at 15 px for every timezone (#24)

Two cuts together keep the productive-time and productive-weekday
titles at the same 15 px the rest of the gallery uses:

1. utcOffsetLabel is now compact. Integer offsets drop the '.00'
   padding ("UTC+7" vs the old "UTC+7.00") and non-integer offsets use
   the colon form ("UTC+5:30", "UTC+5:45"). Saves 3 chars for the
   common integer case, so "Commits by Hour (last year, UTC+7)" lands
   at 34 chars — inside the 15 px budget.

2. weekdayTitle no longer embeds the UTC label. Day-of-week aggregates
   by whole days; clock precision isn't informative there, and
   dropping it shortens the title to 30 chars so the full 15 px lands
   for every timezone.

Quarter-hour-zone users (Kathmandu UTC+5:45) see the hour title drop
to 14 px — 37 chars still exceeds the budget — but that's a rare
case and only 1 px off.

TestUTCOffsetLabel updated to the new format. TestFitTitleFontSize
pinned the new titles.

docs/design-guidelines.md

@@ -70,7 +70,7 @@ When there's **exactly one slice** (one language at 100%), the renderer emits tw
 | Bar fill | `theme.Accent` for the peak bar; `mixHex(Background, Accent, 0.55)` dim for the rest so the busiest period reads at a glance |
 | Y-axis ticks | `niceTicks(max, 5)` — 1/2/5 × 10^k ladder. `last = ceil(max/step) × step` so `yMax ≥ dataMax` always (bars can't poke above chartH into the title) |
 | Axis caption | "hour of day" bottom-center on productive-time; weekday / by-year omit the caption since the x labels are self-describing |
-| Title format | `Commits by Hour (<window>, UTC±N.NN)` / `Commits by Weekday (<window>, UTC±N.NN)` / `Contributions by Year` |
+| Title format | `Commits by Hour (<window>, UTC±H[:MM])` / `Commits by Weekday (<window>)` — weekday drops the UTC so the title always fits at 15 px / `Contributions by Year` |
 | Hover | `<title>HH:00 — N commits</title>` / `<title>Mon — N commits</title>` / `<title>YYYY — N commits</title>` |
 
 ## Heatmap card (contributions-heatmap)

internal/card/card_test.go

@@ -204,9 +204,9 @@ func TestFitTitleFontSize(t *testing.T) {
 		{"Top Starred Repos", 15},
 		{"Most Commit Language (all time)", 15},             // 31 chars
 		{"Contributions by Year", 15},
-		{"Commits by Hour (last year, UTC+7.00)", 14},       // 37 chars
-		{"Commits by Weekday (last year, UTC+7.00)", 13},    // 40 chars
-		{"Commits by Weekday (last year, UTC+12.75)", 12},   // 41 chars
+		{"Commits by Hour (last year, UTC+7)", 15},    // 34 chars, common integer-zone case
+		{"Commits by Hour (last year, UTC+5:45)", 14}, // 37 chars, quarter-hour zone (Kathmandu)
+		{"Commits by Weekday (last year)", 15},         // 30 chars — weekday titles never include UTC
 		{strings.Repeat("x", 200), 11},                       // pathological
 	}
 	for _, c := range cases {
@@ -369,7 +369,7 @@ func adversarialProfile() *github.Profile {
 	p := &github.Profile{
 		Login:                      "user-with-a-very-long-login-name",
 		Name:                       "A Very Long Display Name That Keeps Going",
-		UTCOffsetLabel:             "UTC+12.75", // half-hour / quarter-hour zones widen the title
+		UTCOffsetLabel:             "UTC+12:45", // quarter-hour zone — longest realistic UTC label
 
 		Company:                    "A-Company-With-An-Unusually-Long-Name Pty Ltd",
 		Location:                   "A Place With A Name That Is Way Too Long To Fit",

internal/card/productive_weekday.go

@@ -13,7 +13,7 @@ type productiveWeekdayCard struct{}
 func (productiveWeekdayCard) Filename() string { return "productive-weekday.svg" }
 
 func (productiveWeekdayCard) SVG(p *github.Profile, t theme.Theme) ([]byte, error) {
-	return renderWeekday(weekdayTitle("last year", p.UTCOffsetLabel), p.Weekday, t), nil
+	return renderWeekday(weekdayTitle("last year"), p.Weekday, t), nil
 }
 
 type productiveWeekdayAllTimeCard struct{}
@@ -21,14 +21,14 @@ type productiveWeekdayAllTimeCard struct{}
 func (productiveWeekdayAllTimeCard) Filename() string { return "productive-weekday-all-time.svg" }
 
 func (productiveWeekdayAllTimeCard) SVG(p *github.Profile, t theme.Theme) ([]byte, error) {
-	return renderWeekday(weekdayTitle("all time", p.UTCOffsetLabel), p.WeekdayAllTime, t), nil
+	return renderWeekday(weekdayTitle("all time"), p.WeekdayAllTime, t), nil
 }
 
-func weekdayTitle(window, utcLabel string) string {
-	if utcLabel == "" {
-		return "Commits by Weekday (" + window + ")"
-	}
-	return "Commits by Weekday (" + window + ", " + utcLabel + ")"
+// weekdayTitle skips the UTC offset — the data aggregates into day-of-week
+// buckets, so exact clock precision isn't informative and dropping it keeps
+// the title short enough to render at the full 15 px.
+func weekdayTitle(window string) string {
+	return "Commits by Weekday (" + window + ")"
 }
 
 // Index 0 = Sunday to match time.Weekday (which is what FetchProductive stores).

main.go

@@ -113,13 +113,27 @@ func main() {
 	}
 }
 
-// utcOffsetLabel formats the location's current offset from UTC as "UTC±N.NN"
-// (two-decimal hours) so half-hour zones like India (UTC+5.30) or Nepal
-// (UTC+5.75) render cleanly. Matches github-profile-summary-cards' style.
+// utcOffsetLabel formats the location's current offset from UTC compactly:
+//
+//	integer hours  → "UTC+7"    (no ".00" padding — 3 chars shorter than
+//	                             the old "UTC+7.00" format, keeps the
+//	                             productive-time title at 15 px)
+//	half-hour zone → "UTC+5:30" (India)
+//	quarter-hour   → "UTC+5:45" (Nepal)
+//	negative zone  → "UTC-3"    / "UTC-3:30"
 func utcOffsetLabel(loc *time.Location) string {
 	_, offsetSec := time.Now().In(loc).Zone()
-	hours := float64(offsetSec) / 3600.0
-	return fmt.Sprintf("UTC%+.2f", hours)
+	sign := "+"
+	if offsetSec < 0 {
+		sign = "-"
+		offsetSec = -offsetSec
+	}
+	hours := offsetSec / 3600
+	minutes := (offsetSec % 3600) / 60
+	if minutes == 0 {
+		return fmt.Sprintf("UTC%s%d", sign, hours)
+	}
+	return fmt.Sprintf("UTC%s%d:%02d", sign, hours, minutes)
 }
 
 func resolveThemes(spec string) ([]theme.Theme, error) {

main_test.go

@@ -6,17 +6,17 @@ import (
 	"time"
 )
 
-// TestUTCOffsetLabel checks that half-hour and quarter-hour zones render
-// with a decimal, matching github-profile-summary-cards' "UTC+X.NN" style.
+// TestUTCOffsetLabel checks the compact format: integer hours drop the
+// minutes suffix, non-zero offsets render as `UTC±H:MM`.
 func TestUTCOffsetLabel(t *testing.T) {
 	cases := []struct {
 		zone string
 		want string // must appear in the label; exact value varies by DST
 	}{
-		{"UTC", "UTC+0.00"},
-		{"Asia/Saigon", "UTC+7.00"},
-		{"Asia/Kolkata", "UTC+5.50"},  // half-hour zone
-		{"Asia/Kathmandu", "UTC+5.75"}, // quarter-hour zone
+		{"UTC", "UTC+0"},
+		{"Asia/Saigon", "UTC+7"},
+		{"Asia/Kolkata", "UTC+5:30"},  // half-hour zone
+		{"Asia/Kathmandu", "UTC+5:45"}, // quarter-hour zone
 	}
 	for _, tc := range cases {
 		loc, err := time.LoadLocation(tc.zone)