If whole planets can be shielded in Star Wars, then why couldn't a planet build a huge number of shield generators and protect itself against the Death Star's superlaser?
There are three pieces of evidence, none of which are even remotely conclusive.
Alderaan. The only planet to ACTUALLY be blown up.
There is a long-lasting and bitter arguments among Star Wars fans over whether Alderaan had or did not have a planetary shield, with no meaningful resolution. So, YMMV based on whose side of that argument you agree with.
Some people point to Alderaan's outer sphere lighting up from DS superlaser as evidence of a shield. Other people say it's just atmosphere.
Some people point to A New Hope novelization by Foster, with Vader saying "Despite the Senator's Protests, Alderaan had the strongest defenses in the Empire." . Other people point out that this doesn't necessarily mean a shield. Third people point out that pacifist Alderaan would be unlikely to have OTHER "strong" defenses.
In the Dark Empire Source book it is specifically stated that Alderaan had no shields.
So... you picks your preferred unclear side of the unclear argument and you chooses. If your conclusion is that it had the shields, the answer is "No no shields powerful enough", based on Vader's novelization statement. If your conclusion is that it did not have the shields, the question is basically un-answerable in existing canon.
A second piece of evidence comes from X-Wing books (Michael Stackpole's "Wedge's Gamble")
The facility itself had been built with more demanding specifications than those of any other building on the planet, including the Imperial Palace. Rumor had it that if the Death Star had been used against Imperial Center, the computer center would have been a recognizable and salvageable piece of debris.
This is far from conclusive - first off, it a rumor. Second, while we know that Coruscant has planetary shields from ROTS as well as Thrawn books, this rumor may have implied "assuming we turn off the shields so Death Star CAN fry the planet".
However, you can, from a certain point of view, interpret this evidence as "No no shields powerful enough"
A third piece of evidence is more of a logical conclusion than canon evidence.
Many planets had planetary shields at the time. So if DS couldn't penetrate them, surely Emperor and Tarkin wouldn't be so gung-ho to deploy it?
Almost certainly not
Orson Krennic, one of the main directors of the Death Star project, was convinced that the Death Star was not bothered by planetary shields:
You’re too kind, Governor.” Condescending bastard. “But you express my hopes as well. We’ve seen that the Death Star might destroy a city or a rebel base unimpeded by planetary shields or defense grids. And what you witnessed today? That is only an inkling of the destructive potential—”
Rogue One: A Star Wars Novel
Krennic’s confidence that the Death Star could overcome any planetary shield suggests that they would not present an obstacle. While the state-of-the-art planetary shield on Scarif had fallen by the time the Death Star fired on it, the wording of the previous quote suggests that Jedha might have had one (“we’ve seen that…”).
The junior novelisation for Rogue One would strongly suggest that a high quality Imperial planetary shield (one that Krennic was wholly confident could repulse even the most fearsome barrage that the Rebel fleet could muster) was no match for the Death Star on its lowest setting.
The lights became lasers that fired off together. The thin beams coalesced into a single, massive beam of ultimate destruction aimed straight at the planet.
The blast blew through the shield and began cutting into the planet. Raddus and the rest of the rebel fleet still outside the shield could do nothing but gape at it in horror.
Although some supposition is required (not least because the events of the film were slightly different), it seems likely that on full power, the Death Star should be able to overcome any shields it encounters.