fix(docker): supervised gateway uses --replace to take over stale holder (NS-505) (#47555)

* fix(docker): supervised gateway uses --replace to take over stale holder

Inside the s6 container image the per-profile gateway service rendered a
bare `hermes gateway run` (no --replace). When a gateway is started
OUTSIDE s6 — a stray shell `hermes gateway run`, an agent action, or the
Open WebUI helper (scripts/setup_open_webui.sh) — it grabs the
per-HERMES_HOME PID lock first. The supervised slot then execs the bare
`gateway run`, hits the "Another gateway instance is already running"
guard, exits non-zero, and s6 restarts it: a restart loop that floods the
log every ~12s and never binds. The container looks up but the gateway is
permanently down, and dashboard-only users (no shell) cannot recover.

Render the supervised run script as `gateway run --replace` so s6 is
authoritative for its slot: it reaps the stale holder via the hardened
takeover path (takeover marker + SIGTERM->SIGKILL-with-confirmation +
scoped-lock cleanup in gateway/run.py) and binds. This matches the
systemd service path, which already builds its argv with --replace
(_build_gateway_argv / 'nohup hermes gateway run --replace'), and the
intent already documented in _maybe_redirect_run_to_s6_supervision. The
existing HERMES_S6_SUPERVISED_CHILD sentinel still prevents the
run->start->run redirect recursion. Each profile is scoped to its own
HERMES_HOME and s6 guarantees one supervised instance per slot, so there
is no legitimate supervised sibling for --replace to clobber.

Reported via beta (NS-505): gateway.log showed PID 17907 'running
(manual process)' with the guard error repeating every ~12s on
v2026.6.5.

Adds a regression test asserting every gateway-run exec line in the
rendered script (default + named profile, both privilege branches)
carries --replace, and updates the existing render-script assertion.

* fix(ci): remove stray .venv symlink committed into repo

The PR's commit accidentally tracked a .venv symlink pointing at the
developer's local venv (mode 120000 -> /home/ben/nous/hermes-agent/.venv).
The CI test/e2e/build jobs run `uv venv` to create .venv and failed with
`failed to create directory .venv: File exists (os error 17)` because the
checkout already contained the symlink. All test shards aborted in <15s
during setup, before any test ran.

Untrack the symlink and add a bare `.venv` entry to .gitignore (the
existing `.venv/` rule only matches a directory, so a symlink slipped
through).

.gitignore

@@ -5,6 +5,7 @@
 *.pyc*
 __pycache__/
 .venv/
+.venv
 .vscode/
 .env
 .env.local