fix(operations): repair duplicate json struct tags (S1)

Brief.From/To both serialized as "from" (repeated tag key on one combined
field declaration), and GitSync.Branch/Head/Status all serialized as
"branch" — Go only honors the first `json:"..."` tag on a struct field, so
the second and third tags in `json:"branch" json:"head" json:"status"` were
silently ignored. go vet ./... failed on this; the brief's git state was
unparseable by any client since Head and Status never appeared in the JSON
at all and From/To collided.

Split the combined declarations so each field gets its own tag. go vet
./... now passes clean.

AUDIT.md S1.

internal/operations/operations.go

@@ -13,7 +13,8 @@ import (
 )
 
 type Brief struct {
-	From, To       time.Time          `json:"from"`
+	From           time.Time          `json:"from"`
+	To             time.Time          `json:"to"`
 	Completed      int                `json:"completed"`
 	Failed         int                `json:"failed"`
 	Blocked        int                `json:"blocked"`
@@ -22,7 +23,9 @@ type Brief struct {
 	Git            GitSync            `json:"git_sync"`
 }
 type GitSync struct {
-	Branch, Head, Status string `json:"branch" json:"head" json:"status"`
+	Branch string `json:"branch"`
+	Head   string `json:"head"`
+	Status string `json:"status"`
 }
 
 type StandupItem struct {