feat: add issue view with body cleaning and truncation (task 0003)

Add `issue view <n>` as the first detail command, introducing the
content-cleaning and truncation machinery (src/body.ts) that later issue
and PR slices reuse.

- Default output: number, title, state, author, created, body (truncated
  at 500), plus comment_count; --comments expands every comment (bodies
  truncated at 800); --full suppresses all truncation.
- cleanBody runs only when a body exceeds its limit: normalizes Gitea
  issue/PR URLs on the detected host to Issue#N/PR#N, strips image embeds
  and long URLs, and collapses quoted blocks.
- Type guard: a PR number fails with VALIDATION_ERROR and a `pr view <n>`
  hint, detected via the fetched object's pull_request field.
- renderDetail joins the detail entity, optional sub-blocks, and help.

CLAUDE.md

@@ -3,3 +3,11 @@
 ## Commits
 
 Any commit message you write must follow the Conventional Commits specification as documented in [CONVENTIONAL-COMMITS.md](CONVENTIONAL-COMMITS.md).
+
+## Gotchas
+
+The `origin` remote is a self-hosted **Gitea** instance (`git.alexion.dev`), not GitHub.
+The `gh` CLI does not work here — open pull requests with `tea pr create --login axi --base main --head <branch>`, and list them with `tea pr`.
+
+Task branches are merged into `main` on the remote, so the local `main` goes stale.
+Always `git fetch origin` and cut a task branch from `origin/main`, not from whatever local `main` happens to point at.