flake: replace naersk with crane (#538)

Framework swap, no public API change.

- naersk input → crane (`github:ipetkov/crane`); crane is stateless, no
  nixpkgs.follows needed.
- `forAllSystems` exposes `craneLib = crane.mkLib pkgs`,
  `cargoArtifacts = craneLib.buildDepsOnly` (built once, reused), and
  a shared `nativeBuildInputs = [ pkgs.librsvg pkgs.git ]` consumed by
  buildDepsOnly + buildPackage + cargoClippy so the three derivations
  see the same toolchain shape.
- `packages.default = craneLib.buildPackage` (was naersk-lib.buildPackage)
  with explicit `pname = "hyperhive-workspace"; version = "0.1.0";` —
  the virtual workspace Cargo.toml has no [package].name so crane
  needs the hint.
- `checks.clippy = craneLib.cargoClippy` (was naersk + overrideAttrs
  hack). Crane parses `cargoClippyExtraArgs = "--workspace --all-targets
  -- -D warnings"` correctly; naersk's `mode = "clippy"` used to mangle
  the `--` separator which is why the old wiring went through
  overrideAttrs. The whole hack — including `doCheck = false`,
  `copyTarget = false`, and the swapped buildPhase/installPhase — is
  now gone.
- librsvg native dep (#424) preserved on all three derivations. Added
  pkgs.git too — naersk auto-included it; crane is more minimal, so
  hive-c0re's `lifecycle::tests::setup_proposed_*` (which shell out to
  `git init`+commit) need it explicit to pass under `cargo test` in
  the sandbox.
- build.rs + hive-c0re/Cargo.toml comments updated from "naersk
  derivation" to "crane derivation".
- 3 doc-list-indentation lints in hive-sh4re/src/lib.rs cleaned up
  (replaced `+`-at-line-start with `and`/`/` so doc continuations
  don't trigger `clippy::doc_lazy_continuation`).

Validated locally: `nix build .#default --fallback` succeeds, all
117 tests pass, all four bins in `result/bin/`.

hive-c0re/Cargo.toml

@@ -4,7 +4,7 @@ edition.workspace = true
 version.workspace = true
 # Render branding/agent-configs.svg → $OUT_DIR/agent-configs.png at
 # compile time (#424). build.rs shells out to `rsvg-convert`
-# (librsvg, pulled in via flake.nix' naersk nativeBuildInputs); the
+# (librsvg, pulled in via flake.nix' crane nativeBuildInputs); the
 # baked PNG is included via include_bytes! from forge.rs so no
 # raster gets checked into git.
 build = "build.rs"

hive-c0re/build.rs

@@ -5,7 +5,7 @@
 //! artifact.
 //!
 //! Uses `rsvg-convert` from PATH (librsvg, already available in
-//! nixpkgs and added to the naersk derivation's `nativeBuildInputs`
+//! nixpkgs and added to the crane derivation's `nativeBuildInputs`
 //! in `flake.nix`). For dev builds outside Nix, install librsvg via
 //! your system package manager (Debian/Ubuntu: `librsvg2-bin`,
 //! macOS: `brew install librsvg`).
@@ -43,7 +43,7 @@ fn main() {
             "failed to invoke rsvg-convert: {e}\n\
              install librsvg (Debian/Ubuntu: librsvg2-bin, macOS: brew install librsvg, \
              NixOS: pkgs.librsvg). The Nix derivation already pulls it in via \
-             flake.nix → naersk-lib.buildPackage.nativeBuildInputs.",
+             flake.nix → craneLib.buildPackage.nativeBuildInputs.",
         ),
     }
 }