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-c0re/src/job_queue/mod.rs

@@ -23,7 +23,7 @@
 //! The queue is runtime-only (no persistence): an empty graph on boot; desired
 //! state is re-derived by the reconcile sweep. A single scheduler task
 //! ([`scheduler::run_worker`]) drives it; concurrency comes from the build-slot
-//! capacity, not multiple workers. Design: `docs/scheduler/coordinator.md::Job queue`.
+//! capacity, not multiple workers. Design: `docs/4-implementation/scheduler/coordinator.md::Job queue`.
 
 pub mod exec;
 pub mod model;

hive-c0re/src/job_queue/model.rs

@@ -9,7 +9,7 @@
 //! execution, build-log, cancel, and the dashboard group (a group root's
 //! subtree *is* the group). A DAG used to be a second level above it, with
 //! its own store and its own id; there is no container node any more, so a
-//! job is exactly the nodes it declared. See `docs/scheduler/coordinator.md::Job queue`
+//! job is exactly the nodes it declared. See `docs/4-implementation/scheduler/coordinator.md::Job queue`
 //! for the full design.
 
 pub use hive_host_sock::jobs::State;
@@ -23,7 +23,7 @@ use serde::Serialize;
 ///
 /// What each kind does, the resource/lease rules, and the DAG shapes they
 /// compose into live in the node-inventory table and surrounding sections
-/// of `docs/scheduler/coordinator.md` — this enum is deliberately not a
+/// of `docs/4-implementation/scheduler/coordinator.md` — this enum is deliberately not a
 /// second copy of that; each variant below gets a one-line pointer.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, strum::IntoStaticStr)]
 #[serde(tag = "kind", rename_all = "snake_case")]

hive-c0re/src/job_queue/resource.rs

@@ -16,7 +16,7 @@
 
 /// The resource classes the queue gates concurrency on, as the crate's
 /// generic resource type `R`. What each holds, who declares it, and the
-/// exemptions: see `docs/scheduler/coordinator.md`'s _Scheduler semantics_
+/// exemptions: see `docs/4-implementation/scheduler/coordinator.md`'s _Scheduler semantics_
 /// section — this enum stays the one-line summary, not a second copy.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum Resource {

hive-c0re/src/job_queue/templates.rs

@@ -8,12 +8,12 @@
 //! **The one sanctioned exception is a brace** — a pure-resource-holder root
 //! ([`NodeKind::AgentWindow`]) declaring for a
 //! coordinated subtree whose members then declare nothing. See
-//! `docs/scheduler/coordinator.md`, _Braces_ — which also carries the per-operation DAG
+//! `docs/4-implementation/scheduler/coordinator.md`, _Braces_ — which also carries the per-operation DAG
 //! shapes, so they are not restated here.
 //!
 //! Nodes are **named, not counted** — a template holds the handle
 //! [`JobBuilder::node`] hands back, so an edge says which node it waits on. Why that
-//! removes submit-time cycle validation: `docs/scheduler/coordinator.md`.
+//! removes submit-time cycle validation: `docs/4-implementation/scheduler/coordinator.md`.
 //!
 //! The hive-wide **power ops** (`stop` / `start` / `restart`) are NOT here:
 //! their per-agent shape depends on live running state (an async
@@ -156,7 +156,7 @@ impl<'a> RebuildRoots<'a> {
 
 /// The rebuild node subtree — three group roots (`MetaSync`, the `AgentWindow`
 /// brace, `Reconcile`). `after`, when given, is the node it chains behind. The
-/// shape itself is in `docs/scheduler/coordinator.md`; the code below is the source of
+/// shape itself is in `docs/4-implementation/scheduler/coordinator.md`; the code below is the source of
 /// truth for it, so only the two choices a reader would otherwise undo are
 /// called out here:
 ///

hive-c0re/src/job_queue/tests.rs

@@ -554,7 +554,7 @@ fn rebuild_chain_declares_its_resources_on_the_brace() {
     // ⚠️ **The rename is a reversal, not tidying.** The old name asserted "the
     // slot follows the nix work and the lease follows the container" — each node
     // declaring what it personally needed. The brace inverts that for a
-    // coordinated subtree; see `docs/scheduler/coordinator.md`, _Braces_.
+    // coordinated subtree; see `docs/4-implementation/scheduler/coordinator.md`, _Braces_.
     //
     // (`hive_jobq` owns slot *fairness*, pinned there by
     // `a_contended_resource_goes_to_the_oldest_waiter`. What is c0re's is