SAN JOSE, California — Twitter and other companies have unveiled plans to chop more than 900 Bay Area jobs in a fresh round of tech and biotech layoffs that could jolt the region’s increasingly wobbly economy. In recent days, plans for 913 tech and biotech job cuts — including hundreds more at Twitter — have been revealed in official filings with the state Employment Development Department that this news organization has reviewed. The layoffs affect jobs in San Jose, San Francisco, Milpitas, Mountain View, Pleasanton, Redwood City and South San Francisco, a review of the filings with the EDD s…