HANOI, June 25 — Silent prayer vigils, cautiously worded protest banners and T-shirts pleading for neighbourhoods to be spared — Hanoi residents are showing rare public opposition to a massive redevelopment scheme that could displace hundreds of thousands.Authorities in Vietnam’s capital have been on a demolition blitz, knocking down thousands of homes to make way for bridges and other infrastructure projects as part of a 100-year master plan ap…