Add `pr view <n>` and `pr checks <n>`, built on the truncation machinery
and review fetches from earlier slices.
`pr view` uses the three-call fetch pattern (PR + reviews in parallel, then
the head commit's combined status) so `checks`, `comment_count`, and
`review_count` are in the default output; `--comments`, `--reviews`, and
`--full` behave as on `issue view`, with `--reviews` exposing Gitea's
`official`/`stale` fields plus per-review inline comments.
`pr checks <n>` renders the checks summary line and the `{ name, conclusion }`
rows, or the scalar no-CI message when no statuses exist.
The state→conclusion mapping and summary live in a new `src/checks.ts`;
`commentRows` is extracted into `src/comment.ts` and shared with `issue view`.
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.
