Sækja usage 7.0.2

Two completion fixes: completing a script now uses the same .<script>.usage.kdl sidecar spec that usage exec runs with, and short flags show their help text in completion menus.
Fixed
- (complete) usage complete-word -f <script> now reads a .<script>.usage.kdl file next to the script before falling back to its USAGE comments, the same lookup usage exec already did (#1558, @jdx). Before this, a script with a sidecar completed against the comment spec, or against nothing at all. The bash, zsh and fish scripts from usage generate completion-init call complete-word, so they get the fix without being regenerated. Other usage generate subcommands that take -f <script>, such as completion and markdown, now prefer the sidecar too. When the sidecar doesn't set name or bin, the script's basename is used. Inline specs and stdin input work as before.
- (complete) Short flags now show their help text in completion menus, as long flags already did (#1561, @Ehsan-hash). For flag "-v --verbose" help="Verbose output", completing -v used to show no description and now shows Verbose output. If a root command and a subcommand both define the same short flag, the menu shows the help for the flag that actually applies. Bash completions still list flag names only, with no descriptions.

New Contributors
- @Ehsan-hash made their first contribution in #1561

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