fix(dispatch): detect jj show's positional revset argument

The 0.3.0 help-driven dispatch only scanned a leaf's `Options:` block
for a revset flag. `jj show` takes its revision as a positional
`[REVSET]` argument, not an option, so it looked like it accepted no
revset — and bare `jjf` (which defaults to `show`) errored with
"takes no revset flag" instead of opening the picker.

- Read the `Arguments:` block too: a positional `[REVSET]`/`[REVSETS]`
  that exposes `-r` as an alias is recognized, and jjf injects
  `-r <picked>` for it.
- A bare positional in the passthrough now counts as the user having
  named the revision, so `jjf show @-` bypasses the picker like an
  explicit `-r` would. Option values are stepped over (parsing every
  `Options:` section, including globals) so they aren't mistaken for
  the positional.
- The picker-bypass check also accepts the inline `--revision=<rev>` /
  `--to=<rev>` form, not just space-separated flags.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/main.rs

@@ -68,10 +68,11 @@ fn run_init(mut args: impl Iterator<Item = String>) -> Result<u8> {
 fn run_pick(args: &[String], emit: bool) -> Result<u8> {
     let target = jj::resolve_target(args)?;
 
-    // Case 1: user already supplied a revset flag — bypass the picker entirely
-    // and run their command verbatim. Avoids double-`-r` and respects what
-    // they explicitly asked for.
-    if has_user_revset_flag(&target.passthrough) {
+    // Case 1: user already pinned the revision — a revset flag, or a bare
+    // positional for a positional-revset leaf like `jj show`. Bypass the
+    // picker entirely and run their command verbatim. Avoids double-`-r` and
+    // respects what they explicitly asked for.
+    if target.user_supplied_revset {
         if emit {
             let cmd = jj::command_line(&target, &[]);
             println!("{cmd}");
@@ -132,15 +133,6 @@ fn run_pick(args: &[String], emit: bool) -> Result<u8> {
     }
 }
 
-fn has_user_revset_flag(passthrough: &[String]) -> bool {
-    passthrough.iter().any(|a| {
-        matches!(
-            a.as_str(),
-            "-r" | "--revision" | "--revisions" | "-t" | "--to"
-        )
-    })
-}
-
 #[cfg(unix)]
 fn redirect_stdout_to_tty() -> Result<libc::c_int> {
     use std::os::fd::AsRawFd;