docs: sort the top-level directories into five sections by what the reader wants

Every docs directory moves under 1-getting-started, 2-handbook,
4-implementation or 5-project; the options reference (section 3) comes from
the website and has no directory here. trust-boundary stays whole under the
handbook for now. web-ui, swarm and tools split between handbook and
implementation, and the command-line references move to
2-handbook/reference. Links, path references in code and nix, and the docs
index follow the moves; no page content changes.

hive-forge/src/main.rs

@@ -229,7 +229,7 @@ fn run() -> Result<()> {
     }
     // Same reasoning as `credential-helper` above: no repo, no forge
     // credentials — just a pure render of the clap tree the docs build
-    // pipes into `docs/tools/forge-cli.md`.
+    // pipes into `docs/2-handbook/reference/forge-cli.md`.
     if let Verb::MarkdownDocs = verb {
         // `show_footer(false)`: the default footer's wording ("This
         // document was generated automatically by...") is clap-markdown's

hive-forge/src/verbs/ci_rerun.rs

@@ -14,7 +14,7 @@
 //! given handle:
 //! - `--pr <n>` → refuses instead of dispatching: a `workflow_dispatch` run
 //!   writes no commit status, so it cannot clear a red `(pull_request)`
-//!   check on the PR's sha — see `docs/scheduler/ci.md`'s "CI checks" for
+//!   check on the PR's sha — see `docs/4-implementation/scheduler/ci.md`'s "CI checks" for
 //!   why. Re-run from the web UI instead.
 //! - `--branch <name>` → dispatches `--workflow` on that branch directly.
 //! - `--run <n>` → looks the run up by its display number (same convention