nginx: Set X-Frame-Options header to DENY.
nginx: Set X-Frame-Options header to DENY.

While there are legitimate use cases for embedded Zulip in an iFrame,
they're rare, and it's more important to prevent this category of
attack by default.

Sysadmins can switch this to a whitelist when they want to use frames.

punchagan/zulip,synicalsyntax/zulip,kou/zulip,rishig/zulip,rht/zulip,rishig/zulip,eeshangarg/zulip,showell/zulip,jackrzhang/zulip,andersk/zulip,shubhamdhama/zulip,tommyip/zulip,timabbott/zulip,rht/zulip,showell/zulip,zulip/zulip,zulip/zulip,dhcrzf/zulip,punchagan/zulip,timabbott/zulip,tommyip/zulip,hackerkid/zulip,hackerkid/zulip,synicalsyntax/zulip,shubhamdhama/zulip,andersk/zulip,kou/zulip,jackrzhang/zulip,brainwane/zulip,shubhamdhama/zulip,tommyip/zulip,showell/zulip,dhcrzf/zulip,synicalsyntax/zulip,timabbott/zulip,andersk/zulip,dhcrzf/zulip,eeshangarg/zulip,andersk/zulip,dhcrzf/zulip,zulip/zulip,timabbott/zulip,punchagan/zulip,shubhamdhama/zulip,punchagan/zulip,rishig/zulip,brainwane/zulip,showell/zulip,tommyip/zulip,tommyip/zulip,rht/zulip,synicalsyntax/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip,jackrzhang/zulip,eeshangarg/zulip,tommyip/zulip,brainwane/zulip,tommyip/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,jackrzhang/zulip,shubhamdhama/zulip,jackrzhang/zulip,hackerkid/zulip,rishig/zulip,rishig/zulip,hackerkid/zulip,zulip/zulip,zulip/zulip,andersk/zulip,rishig/zulip,jackrzhang/zulip,dhcrzf/zulip,rishig/zulip,hackerkid/zulip,brainwane/zulip,eeshangarg/zulip,kou/zulip,brainwane/zulip,synicalsyntax/zulip,jackrzhang/zulip,rht/zulip,timabbott/zulip,synicalsyntax/zulip,dhcrzf/zulip,punchagan/zulip,rht/zulip,timabbott/zulip,synicalsyntax/zulip,brainwane/zulip,andersk/zulip,showell/zulip,hackerkid/zulip,dhcrzf/zulip,zulip/zulip,punchagan/zulip,shubhamdhama/zulip,shubhamdhama/zulip,eeshangarg/zulip,timabbott/zulip,brainwane/zulip,showell/zulip,eeshangarg/zulip,punchagan/zulip,kou/zulip,kou/zulip,showell/zulip