feat: add pr view and checks (task 0009)

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`.

src/render.ts

@@ -45,6 +45,17 @@ export function renderList(options: RenderListOptions): string {
   return [options.countLine, body, encode({ help: options.help })].join("\n");
 }
 
+/**
+ * A literal `noun: value` line followed by the help block — for output whose
+ * entity is a single line rather than a field map or a list (e.g. the no-CI
+ * `checks:` message). The value is emitted verbatim, not re-encoded: TOON reads
+ * a string scalar to end of line, so a comma-bearing message stays unquoted,
+ * matching the way a summary line stands above a list block.
+ */
+export function renderScalar(noun: string, value: string, help: string[]): string {
+  return [`${noun}: ${value}`, encode({ help })].join("\n");
+}
+
 /** A secondary list block appended below a detail entity (e.g. comments). */
 export interface DetailBlock {
   noun: string;