feat(#1877): restructure hive-forge into pr/issue sub-verbs

Group issue/PR operations under `pr` and `issue` parent commands
(`hive-forge pr close 42`, `issue create …`, `pr status --pr 42`) per the
operator decision — kind-namespaced verbs replace the flat surface.

- new `verbs::pr_cmd` / `verbs::issue_cmd` parent commands wrap the existing
  per-verb modules (reuse their Args + run fns) under `#[command(subcommand)]`.
- kind-validation (the win over the old generic verbs): the generics that work
  on both (view/comment/comments/close/labels/assign/timeline) call
  `assert_kind` first, so `pr close <issue>` / `issue close <pr>` are rejected
  with a 'use the other command' message. PR-only / issue-only verbs are
  kind-correct by construction. `number` exposed `pub(crate)` on the shared
  verbs so the wrappers can probe it.
- every flat kind verb (`close`, `pr-create`, `pr-status`, `issue-edit`, …)
  kept as a `#[command(hide = true)]` back-compat alias — still parses, dropped
  from --help; removed in a later sweep once usage migrates. (`pr`/`issue`
  bare-show become `pr show` / `issue show` — the names are now parents.)
- docs/tools/forge.md documents the new surface + the deprecated aliases.

cargo build/clippy/fmt clean, 54 tests pass; --help surface + alias parsing
smoke-tested.

hive-forge/src/verbs/comments.rs

@@ -31,7 +31,7 @@ const PAGE_SIZE: usize = 50;
 #[derive(ClapArgs)]
 pub struct Args {
     /// Issue or PR number.
-    number: u64,
+    pub(crate) number: u64,
     /// Page size for the head-of-thread shape (Forgejo caps at 50).
     /// Mutually exclusive with `--tail`.
     #[arg(long, default_value_t = 50, conflicts_with = "tail")]