docs(config): name every template variable format_path builds (#3782)

Found by the nightly survey while reviewing
`src/config/user/accessors.rs`.

`UserConfig::format_path`'s `# Arguments` block doesn't match what the
function builds. It documents `{{ main_worktree }}`, `{{ branch }}`, and
`{{ owner }}`, and describes the `repo` parameter as being for "template
function access" — but the function also inserts `{{ repo }}` (from
`main_worktree`, not from `repo`) and `{{ repo_path }}` (read off
`repo`). Both omissions are in `default_worktree_path()` in the same
file — `"{{ repo_path }}/../{{ repo }}.{{ branch | sanitize }}"` — so
the docstring omits two of the three variables the default template
uses.

The `{{ owner }}` line was also a bare bullet in the middle of the
parameter list, describing a template variable rather than an argument,
and it didn't note that `owner` is only inserted when
`primary_remote_parsed_url()` returns a URL it can parse.

This corrects the parameter descriptions, moves the template-variable
note out of the argument list, and links the user-facing variable list
at
[worktrunk.dev/config](https://worktrunk.dev/config/#worktree-path-template)
rather than duplicating it here (verified: the page returns 200 and
carries that anchor).

No test: the change is a doc comment only, with no behavior to exercise.
`cargo fmt --check` and `cargo doc --no-deps -p worktrunk` are clean.

Co-authored-by: worktrunk-bot <254187624+worktrunk-bot@users.noreply.github.com>

Author: worktrunk-bot

src/config/user/accessors.rs

@@ -229,12 +229,18 @@ impl UserConfig {
     /// Format a worktree path using this configuration's template.
     ///
     /// # Arguments
-    /// * `main_worktree` - Main worktree directory name (replaces {{ main_worktree }} in template)
+    /// * `main_worktree` - Main worktree directory name; supplies both
+    ///   `{{ main_worktree }}` and `{{ repo }}`
     /// * `branch` - Branch name (replaces {{ branch }} in template; use `{{ branch | sanitize }}` for paths)
-    /// * `repo` - Repository for template function access
-    /// * remote owner/namespace is available as {{ owner }}
+    /// * `repo` - Repository, for template function access and for the
+    ///   `{{ repo_path }}` and `{{ owner }}` values read off it —
+    ///   `{{ owner }}` is absent when the primary remote has no parseable URL
     /// * `project` - Optional project identifier (e.g., "github.com/user/repo") to look up
     ///   project-specific worktree-path template
+    ///
+    /// The default template uses `{{ repo_path }}`, `{{ repo }}`, and
+    /// `{{ branch | sanitize }}`; the full user-facing list is in
+    /// [the config docs](https://worktrunk.dev/config/#worktree-path-template).
     pub fn format_path(
         &self,
         main_worktree: &str,