svc-selkies: honor SELKIES_MODE env var in run script

[DL6ER]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

Replace the hardcoded --mode="websockets" in the svc-selkies s6 run script with --mode="${SELKIES_MODE:-websockets}", in both the production exec and the DEV_MODE branch.

Benefits of this PR and context:

Selkies declares a mode setting with env_var: SELKIES_MODE (see src/selkies/settings.py):

{'name': 'mode', 'type': 'str', 'default': 'websockets',
 'env_var': 'SELKIES_MODE',
 'help': "Specify the mode: 'webrtc' or 'websockets'; defaults to websockets"}

But because the run script passes --mode="websockets" on the command line, the hardcoded value wins over the env var. Setting -e SELKIES_MODE=webrtc on the container has no effect; users have to either patch the run script at runtime or live-edit the compiled /run/service/svc-selkies/run.

After this change, the env var works as documented: the default behaviour stays websockets while -e SELKIES_MODE=webrtc actually selects WebRTC mode at startup. Combined with the dual-mode supervisor (separate PRs), this lets users choose the initial mode declaratively.

How Has This Been Tested?

docker run -d -e SELKIES_MODE=webrtc ... webtop:patched
docker exec <id> ps -o pid,cmd | grep selkies
> /lsiopy/bin/python3 /lsiopy/bin/selkies --addr=localhost --mode=webrtc

Without env var:

docker run -d ... webtop:patched
docker exec <id> ps -o pid,cmd | grep selkies
> /lsiopy/bin/python3 /lsiopy/bin/selkies --addr=localhost --mode=websockets

Default behaviour preserved.

Source / References:

• Setting definition: selkies-project/selkies src/selkies/settings.py, field mode with env_var: SELKIES_MODE.
• Affected file in this repo: root/etc/s6-overlay/s6-rc.d/svc-selkies/run.

[Copilot]

Pull request overview

This PR updates the svc-selkies s6 run script so Selkies’ startup mode can be configured via the documented SELKIES_MODE environment variable instead of being overridden by a hardcoded CLI flag.

Changes:

• Replace hardcoded --mode="websockets" with --mode="${SELKIES_MODE:-websockets}" in the DEV_MODE (nodemon) launch path.
• Replace hardcoded --mode="websockets" with --mode="${SELKIES_MODE:-websockets}" in the production exec launch path.

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[LinuxServer-CI]

I am a bot, here are the test results for this PR:
https://ci-tests.linuxserver.io/lspipepr/selkies-base/debiantrixie-aa141909-pkg-aa141909-dev-bf75ba339e1336f269106f2443b9cd22d9fca37a-pr-152/index.html
https://ci-tests.linuxserver.io/lspipepr/selkies-base/debiantrixie-aa141909-pkg-aa141909-dev-bf75ba339e1336f269106f2443b9cd22d9fca37a-pr-152/shellcheck-result.xml

Tag	Passed
amd64-debiantrixie-aa141909-pkg-aa141909-dev-bf75ba339e1336f269106f2443b9cd22d9fca37a-pr-152	✅
arm64v8-debiantrixie-aa141909-pkg-aa141909-dev-bf75ba339e1336f269106f2443b9cd22d9fca37a-pr-152	✅