fix(time): accept spaced durations and print whole-second times

tea time create 1 1h25m printed 2026-10-11T18:57:49.588823137Z while time
list printed whole seconds, and "1h 30m" or 2d failed with "duration
must be nonzero whole seconds". Durations may now contain spaces, and
errors name the problem: "invalid duration "2d": use h, m and s units
such as 1h25m". Tracked times are whole seconds everywhere.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/validation_test.go

@@ -211,8 +211,8 @@ func TestUsageErrorsPrecedeRequests(t *testing.T) {
 		{[]string{"team", "member", "add", "invalid", "alice"}, `invalid team "invalid": use ORG/TEAM, such as acme/developers, or a team ID`},
 		{[]string{"team", "view", "acme/"}, `invalid team "acme/"`},
 		{[]string{"team", "repo", "add", "2", "service", "-R", "acme/service"}, "--repo is not used by tea team repo add"},
-		{[]string{"time", "create", "1", "0s"}, "duration must be nonzero whole seconds, for example 1h25m"},
-		{[]string{"time", "create", "1", "1ms"}, "duration must be nonzero whole seconds, for example 1h25m"},
+		{[]string{"time", "create", "1", "0s"}, `invalid duration "0s": time spent must be positive`},
+		{[]string{"time", "create", "1", "1ms"}, `invalid duration "1ms": use whole seconds`},
 		{[]string{"time", "list", "--issue", "0"}, "--issue must be positive"},
 		{[]string{"time", "list", "--mine", "--issue", "1"}, "--mine, --issue and --username select mutually exclusive scopes"},
 		{[]string{"time", "list", "--from", "2026-10-02", "--until", "2026-10-01"}, "--from must not be later than --until"},