feat: add pr list (task 0008)

Implements `pr list` with the two policies later PR slices reuse:
client-side filtering with the filtered-set count line (ADR 0005) and
the official-first reviewDecision via parallel per-PR review fetches
(ADR 0006), extracted into src/review.ts.

API-supported flags map to their params (--state, --author→poster,
--label name→ID, --label-id, --sort, --limit, --fields); --assignee,
--base, --head, and --draft filter in-process after full pagination,
with the count line's total taken from the filtered set. --search is
refused with a redirect to `search prs`.

Adds a boolText field extractor and a shared parsePositiveInt helper,
the latter also adopted by issue list's --limit parsing.

src/fields.ts

@@ -32,6 +32,20 @@ export function lowercased<T>(name: string, path: string = name): FieldDef<T> {
   };
 }
 
+/**
+ * Render a boolean field as one of two words (default `yes`/`no`). A missing or
+ * falsy value reads as the `no` text, so an absent `draft` flag is reported as
+ * the ordinary non-draft it represents rather than blank.
+ */
+export function boolText<T>(
+  name: string,
+  path: string = name,
+  yes = "yes",
+  no = "no",
+): FieldDef<T> {
+  return { name, extract: (raw) => (pluckPath(raw, path) ? yes : no) };
+}
+
 /**
  * Join a field holding an array of objects (labels, assignees) into a single
  * string of each element's `key` property.