feat(cli): alias gen for generate subcommand + add -l / -w short flags

clap alias makes both `relicario gen -l 32` and the long-form
`relicario generate -l 32` route to the same handler. The short flags
-l (length) and -w (words) were missing -- the READMEs existing example
`relicario generate -l 32` only actually worked after this commit.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/relicario-cli/src/main.rs

@@ -140,12 +140,13 @@ enum Commands {
     /// vault, falls back to `settings generator-defaults` for unspecified
     /// flags; outside a vault, uses built-in defaults (length 20, safe
     /// symbol set, 5 BIP39 words, space separator).
+    #[command(alias = "gen")]
     Generate {
-        #[arg(long)]
+        #[arg(short = 'l', long)]
         length: Option<u32>,
         #[arg(long)]
         bip39: bool,
-        #[arg(long)]
+        #[arg(short = 'w', long)]
         words: Option<u32>,
         #[arg(long)]
         symbols: Option<String>,