fix(config): print only the value of config get and add display preferences

tea config get printed "key<TAB>value", so $(tea config get editor) was
not usable; it now prints the value alone, and --show-source appends the
source (D18). config get reads the instance's user, and instance settings
come from the selected instance (--host, TEA_HOST, default_host or the
sole instance). Unknown keys list the valid ones, and keys that need
--host or --user say so. config path no longer loads the settings, so it
works when hosts.yml is broken. config list is a table on a terminal.
config set confirms the change on a terminal and warns when default_host
has no account.

config.yml stores the hyperlinks (auto, always, never) and markdown
(auto, raw) preferences that tables and views now read, instead of the
TEA_HYPERLINKS and TEA_MARKDOWN variables. The environment table moves
out of tea config --help into tea help environment.

alias set refuses to replace an alias without --clobber, drops a leading
"tea", and explains how to quote an expansion with spaces or flags.
alias delete takes several names or --all, alias list is a table, and
an empty list says so on a terminal.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/completion.go

@@ -255,15 +255,6 @@ func (a *application) completeAliases(_ *cobra.Command, _ []string, toComplete s
 	return matching(describe(slices.Sorted(maps.Keys(aliases)), func(name string) (string, string) { return name, aliases[name] }), toComplete), cobra.ShellCompDirectiveNoFileComp
 }
 
-// configValues lists the values of the settings that accept a fixed set.
-var configValues = map[string][]string{
-	"git_protocol": {"https", "ssh"},
-	"prompt":       {"enabled", "disabled"},
-	"color":        {"auto", "always", "never"},
-	"insecure":     {"true", "false"},
-	"ssh_agent":    {"true", "false"},
-}
-
 // completeConfig completes a setting name, then its value: the fixed values, the configured instances
 // for default_host, or the Git remotes for remote.
 func (a *application) completeConfig(cmd *cobra.Command, args []string, toComplete string) ([]cobra.Completion, cobra.ShellCompDirective) {