feat: add streamd daily command

`streamd daily [YYYYMMDD]` opens the earliest existing daily file
(file_type=daily) whose timestamp falls within the target date.
If no such file exists it creates `<timestamp>_daily.md` and opens it.
Date defaults to today in the repository timezone.

src/main.rs

@@ -18,6 +18,7 @@ fn main() -> miette::Result<()> {
         Some(Commands::Timesheet { decimal, debug }) => {
             streamd::cli::commands::timesheet::run(decimal, debug)?
         }
+        Some(Commands::Daily { date }) => streamd::cli::commands::daily::run(date)?,
         Some(Commands::Completions { shell }) => {
             streamd::cli::commands::completions::run(shell);
         }