Here’s a “moving picture” in the true sense, a movie that suspends disbelief by making the silver screen into a portal. Celia (Mia Farrow) is a sad-faced moonstruck waitress in Depression-era New Jersey. Hollywood gossip is her grist. Her escape from drudgery is watching dapper young matinee idol Tom Baxter (Jeff Daniels) in the movie “The Purple Rose of Cairo.” If only he were real! Be careful what you wish for. Suddenly, Tom escapes both screenplay and screen and walks into Celia’s life. Muddled Celia is saddled with her bewildered hero, an unfinished movie, and — in a bit of Woody Allen mischief — the actor Gil Shepard, who plays Tom in “Purple Rose.” Literal escapism has never been so charming and bittersweet. One of Allen’s most tender if overlooked undertakings.