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/pr_cmd.rs

@@ -0,0 +1,93 @@
+//! `pr <verb>` — PR-scoped sub-commands. Wraps the per-verb modules under a
+//! `pr` parent so `hive-forge pr close 42`, `pr status --pr 42`, etc. read as
+//! kind-namespaced commands. The generic verbs that also work on issues
+//! (view/comment/comments/close/labels/assign/timeline) kind-check the number
+//! is a PR first (`assert_kind`); the PR-only verbs hit `/pulls/…` and are
+//! kind-correct by construction. The flat `pr-*` + bare generic verbs stay as
+//! hidden back-compat aliases (see `main.rs`).
+
+use anyhow::Result;
+use clap::{Args as ClapArgs, Subcommand};
+
+use crate::client::Client;
+use crate::verbs::{self, Kind, assert_kind};
+
+#[derive(ClapArgs)]
+pub struct Args {
+    #[command(subcommand)]
+    cmd: Cmd,
+}
+
+#[derive(Subcommand)]
+enum Cmd {
+    /// Show PR metadata as JSON.
+    Show(verbs::pr::Args),
+    /// List the PR's commits as JSON.
+    Commits(verbs::pr_commits::Args),
+    /// Create a pull request.
+    Create(verbs::pr_create::Args),
+    /// PR health view: mergeable / CI / reviews.
+    Status(verbs::pr_status::Args),
+    /// Merge the PR.
+    Merge(verbs::pr_merge::Args),
+    /// List a PR's reviews, or submit one.
+    Reviews(verbs::pr_reviews::Args),
+    /// Print the PR's unified diff.
+    Diff(verbs::diff::Args),
+    /// Show title + body + comments.
+    View(verbs::view::Args),
+    /// Post a comment on the PR.
+    Comment(verbs::comment::Args),
+    /// List comments on the PR.
+    Comments(verbs::comments::Args),
+    /// Close the PR.
+    Close(verbs::close::Args),
+    /// List / add / remove labels.
+    Labels(verbs::labels::Args),
+    /// Assign or unassign a user.
+    Assign(verbs::assign::Args),
+    /// List timeline events.
+    Timeline(verbs::timeline::Args),
+}
+
+pub fn run(client: &Client, args: Args) -> Result<()> {
+    match args.cmd {
+        // PR-only verbs — kind-correct by construction (hit `/pulls/…`).
+        Cmd::Show(a) => verbs::pr::run(client, a),
+        Cmd::Commits(a) => verbs::pr_commits::run(client, a),
+        Cmd::Create(a) => verbs::pr_create::run(client, a),
+        Cmd::Status(a) => verbs::pr_status::run(client, a),
+        Cmd::Merge(a) => verbs::pr_merge::run(client, a),
+        Cmd::Reviews(a) => verbs::pr_reviews::run(client, a),
+        Cmd::Diff(a) => verbs::diff::run(client, a),
+        // Generics shared with `issue` — verify the number is a PR first.
+        Cmd::View(a) => {
+            assert_kind(client, a.number, Kind::Pr)?;
+            verbs::view::run(client, a)
+        }
+        Cmd::Comment(a) => {
+            assert_kind(client, a.number, Kind::Pr)?;
+            verbs::comment::run(client, a)
+        }
+        Cmd::Comments(a) => {
+            assert_kind(client, a.number, Kind::Pr)?;
+            verbs::comments::run(client, a)
+        }
+        Cmd::Close(a) => {
+            assert_kind(client, a.number, Kind::Pr)?;
+            verbs::close::run(client, a)
+        }
+        Cmd::Labels(a) => {
+            assert_kind(client, a.number, Kind::Pr)?;
+            verbs::labels::run(client, a)
+        }
+        Cmd::Assign(a) => {
+            assert_kind(client, a.number, Kind::Pr)?;
+            verbs::assign::run(client, a)
+        }
+        Cmd::Timeline(a) => {
+            assert_kind(client, a.number, Kind::Pr)?;
+            verbs::timeline::run(client, a)
+        }
+    }
+}