Add Go patterns cheat sheet

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

go-cheatsheet.md

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+# Go Patterns Cheat Sheet
+
+## Defer - Cleanup Pattern
+```go
+initDB()
+defer db.Close()  // Runs when function exits, no matter how
+```
+- Schedules function to run when surrounding function returns
+- Executes in LIFO order if multiple defers
+- Great for resource cleanup (files, connections, etc.)
+
+## Formatted Output to HTTP
+```go
+fmt.Fprintf(w, "%d", rng.Intn(1000))
+```
+- `fmt.Fprintf` = formatted print to a writer (not stdout)
+- `w` = HTTP response writer
+- `%d` = format placeholder for integers
+- Alternative: `fmt.Fprint(w, value)` for no formatting
+
+## Ticker + Select for Scheduled Tasks
+```go
+func startMiningTicker() {
+    ticker := time.NewTicker(1 * time.Minute)
+    defer ticker.Stop()
+    
+    for {
+        select {
+        case <-ticker.C:
+            updateMiningValue()
+        }
+    }
+}
+```
+- `time.NewTicker()` creates repeating timer
+- `select` waits for channel events
+- `<-ticker.C` receives from ticker's channel
+- Common pattern for background jobs
+
+## Database Scanning into Structs
+```go
+type MiningRecord struct {
+    ID        int       `json:"id"`
+    Timestamp time.Time `json:"timestamp"`
+    Value     float64   `json:"value"`
+    Rate      float64   `json:"rate"`
+}
+
+var latest MiningRecord
+err := db.QueryRow("SELECT id, timestamp, value, rate FROM mining ORDER BY timestamp DESC LIMIT 1").
+    Scan(&latest.ID, &latest.Timestamp, &latest.Value, &latest.Rate)
+```
+- `Scan()` copies SQL results into Go variables
+- Order matters: first column → first Scan argument
+- Use `&` to pass addresses so Scan can write to them
+- Struct tags (`json:"id"`) control JSON serialization
+
+## Blank Identifier for Ignoring Values
+```go
+_, err = db.Exec("INSERT INTO mining (timestamp, value, rate) VALUES (?, ?, ?)", now, newValue, latest.Rate)
+```
+- `_` = blank identifier, discards unwanted return values
+- `db.Exec()` returns `(sql.Result, error)`
+- We only care about the error, so ignore the Result
+- Go requires this instead of leaving variables unused
+
+## HTTP Handler Pattern
+```go
+func handler(w http.ResponseWriter, r *http.Request) {
+    // w = where response goes
+    // r = incoming request data
+    fmt.Fprintf(w, "response")
+}
+```
+- `w` writes back to client
+- `r` contains request info
+- Common to use `fmt.Fprintf(w, ...)` for simple responses