Standardize daemon detection with tryDaemonLock probe (bd-wgu4)

- Extract lock checking to internal/lockfile package
- Add lock probe in RPC client before connection attempts
- Update daemon discovery to use lock probe
- Eliminates unnecessary connection attempts when socket missing

Closes bd-wgu4

Amp-Thread-ID: https://ampcode.com/threads/T-3b863f21-3af4-49d3-9214-477d904b80fe
Co-authored-by: Amp <amp@ampcode.com>

internal/lockfile/lock_wasm.go

@@ -0,0 +1,17 @@
+//go:build js && wasm
+
+package lockfile
+
+import (
+	"errors"
+	"fmt"
+	"os"
+)
+
+var errDaemonLocked = errors.New("daemon lock already held by another process")
+
+func flockExclusive(f *os.File) error {
+	// WASM doesn't support file locking
+	// In a WASM environment, we're typically single-process anyway
+	return fmt.Errorf("file locking not supported in WASM")
+}