ui: can't copy-paste custom chart links

**Describe the problem**

The following doesn't work:

- make custom chart
- copy resulting URL, for example: http://some-host.com:26258/#/debug/chart?preset=past-30-minutes&charts=%5B%7B%22metrics%22%3A%5B%7B%22downsampler%22%3A1%2C%22aggregator%22%3A2%2C%22derivative%22%3A2%2C%22perSource%22%3Atrue%2C%22perTenant%22%3Afalse%2C%22nodeSource%22%3A%22%22%2C%22tenantSource%22%3A%22%22%2C%22metric%22%3A%22cr.node.sys.host.net.send.tcp.retrans_segs%22%7D%5D%2C%22axisUnits%22%3A0%7D%2C%7B%22metrics%22%3A%5B%7B%22downsampler%22%3A1%2C%22aggregator%22%3A2%2C%22derivative%22%3A2%2C%22perSource%22%3Atrue%2C%22perTenant%22%3Afalse%2C%22nodeSource%22%3A%22%22%2C%22tenantSource%22%3A%22%22%2C%22metric%22%3A%22cr.node.sys.host.net.recv.drop%22%7D%2C%7B%22downsampler%22%3A1%2C%22aggregator%22%3A2%2C%22derivative%22%3A2%2C%22perSource%22%3Atrue%2C%22perTenant%22%3Afalse%2C%22nodeSource%22%3A%22%22%2C%22tenantSource%22%3A%22%22%2C%22metric%22%3A%22cr.node.sys.host.net.recv.err%22%7D%5D%2C%22axisUnits%22%3A0%7D%2C%7B%22metrics%22%3A%5B%7B%22downsampler%22%3A1%2C%22aggregator%22%3A2%2C%22derivative%22%3A2%2C%22perSource%22%3Atrue%2C%22perTenant%22%3Afalse%2C%22nodeSource%22%3A%22%22%2C%22tenantSource%22%3A%22%22%2C%22metric%22%3A%22cr.node.sys.host.net.send.drop%22%7D%2C%7B%22downsampler%22%3A1%2C%22aggregator%22%3A2%2C%22derivative%22%3A2%2C%22perSource%22%3Atrue%2C%22perTenant%22%3Afalse%2C%22nodeSource%22%3A%22%22%2C%22tenantSource%22%3A%22%22%2C%22metric%22%3A%22cr.node.sys.host.net.send.err%22%7D%5D%2C%22axisUnits%22%3A0%7D%2C%7B%22metrics%22%3A%5B%7B%22downsampler%22%3A1%2C%22aggregator%22%3A2%2C%22derivative%22%3A2%2C%22perSource%22%3Atrue%2C%22perTenant%22%3Afalse%2C%22nodeSource%22%3A%22%22%2C%22tenantSource%22%3A%22%22%2C%22metric%22%3A%22cr.node.sys.host.net.send.bytes%22%7D%2C%7B%22downsampler%22%3A1%2C%22aggregator%22%3A2%2C%22derivative%22%3A2%2C%22perSource%22%3Atrue%2C%22perTenant%22%3Afalse%2C%22nodeSource%22%3A%22%22%2C%22tenantSource%22%3A%22%22%2C%22metric%22%3A%22cr.node.sys.host.net.recv.bytes%22%7D%5D%2C%22axisUnits%22%3A1%7D%5D
- try to open the same custom chart link on another cluster (even with identical binary version and all other configuration same)

Get "Something went wrong." and the following error in console

This makes it hard to reuse custom charts.

Last seen on `f6e9d3fd43f Merge #149948` today, but it's bugged me a few times in the past, too, so it isn't a brand new issue. Speculatively assigning branch labels for 25.2 and 25.3, but probably also broken in 25.1.

Jira issue: CRDB-52634

No source file or test is named. Start by reproducing the reported custom-chart URL flow across two clusters, then inspect the browser console error shown in the report. Done means the copied custom chart link opens successfully on another cluster with equivalent configuration.

Written by the indexing model from the issue text.