docs: the manage examples pass the password with --password #915

extenddb manage reads the password from EXTENDDB_PASSWORD when --password is absent, and #849 makes it print a warning on stderr when it gets the flag. On main at 35edb77, 12 files show manage taking the password with the flag, in 121 lines. A line counts when it has manage and --password, or when it continues a manage command with --password:

Commands in the .agents references run as written, so those three commands put real passwords on the command line.

Suggested change: set the variable once in each section without echo, with read -rs EXTENDDB_PASSWORD; export EXTENDDB_PASSWORD, and drop --password from the examples. An inline EXTENDDB_PASSWORD=... extenddb manage ... keeps the password out of process listings. The line still goes into shell history, so the examples should not use that form either.

Raised in the review of #849.