fix(rpm): rename neuron package to helexa-neuron

Fedora's official repos ship a package named `neuron` — the NEURON
neural-simulation environment from Yale (see
https://src.fedoraproject.org/rpms/neuron). Having our own `neuron`
in the helexa COPR caused dnf5 to silently no-op `dnf install neuron`
because of the name collision, even with the COPR repo enabled and
keys imported. The only workarounds were full NEVRA (`dnf install
neuron-0.1.12-1.fc43.x86_64`) or a local file install — neither
acceptable for end-users.

Rename the RPM package to `helexa-neuron`. Keep binary (/usr/bin/neuron),
systemd unit (neuron.service), system user (neuron), and config dir
(/etc/neuron) unchanged — those are project-local contexts where the
short name is unambiguous. Follows Fedora subpackage-style naming
except with a vendor prefix rather than a parent-package prefix,
because neuron is an independent package from cortex (installed on
different hosts) and neither depends on the other.

Changes:
- neuron.spec -> helexa-neuron.spec (git rename)
- Name: neuron -> helexa-neuron (with comment explaining why)
- CI: srpm-neuron job now builds helexa-neuron-VERSION.tar.gz with the
  matching top-level dir prefix, publishes to helexa/helexa-neuron COPR
- CI: bump-version job references helexa-neuron.spec
- CLAUDE.md: install instructions updated

Old helexa/neuron COPR project can be deleted after the first
helexa/helexa-neuron build lands.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -596,15 +596,18 @@ Completed. Both packages have RPM specs, systemd units, and example configs.
 CI builds parallel SRPMs on tag push and publishes to separate COPR repos.
 
 - `cortex.spec` → `helexa/cortex` COPR: binary, systemd unit, config files
-- `neuron.spec` → `helexa/neuron` COPR: binary, systemd unit, config
+- `helexa-neuron.spec` → `helexa/helexa-neuron` COPR: binary, systemd unit,
+  config. Package renamed from `neuron` to avoid collision with Fedora's
+  NEURON neural-simulation package (https://src.fedoraproject.org/rpms/neuron);
+  binary, systemd unit, system user, and config dir stay as `neuron`.
 - `data/cortex.service`, `data/neuron.service` — systemd units
 - `cortex.example.toml`, `neuron.example.toml`, `models.example.toml`
 - CI: parallel `srpm-cortex` + `srpm-neuron` jobs, then parallel COPR publish
 
 Install:
 ```sh
-dnf copr enable helexa/cortex && dnf install cortex    # gateway host
-dnf copr enable helexa/neuron && dnf install neuron    # GPU nodes
+dnf copr enable helexa/cortex && dnf install cortex                    # gateway host
+dnf copr enable helexa/helexa-neuron && dnf install helexa-neuron      # GPU nodes
 ```
 
 ### Phase 11: llama.cpp harness stub