Add basic password auth to the reduction dashboard

[Copilot]

Adds minimal basic auth to the Panel dashboard using environment variables LIVEDATA_BASIC_AUTH_PASSWORD and LIVEDATA_BASIC_AUTH_COOKIE_SECRET. Accepts any username with the configured password.

Changes

• DashboardBase: Added basic_auth_password and basic_auth_cookie_secret params, passed to pn.serve() in both server property and run_forever()
• Validation: Both params must be provided together or neither—raises ValueError on partial config
• reduction.py: Added CLI args --basic-auth-password and --basic-auth-cookie-secret with security warning recommending env vars

Auth options are scoped to the dashboard layer per review feedback (not in generic Service class).

Usage

export LIVEDATA_BASIC_AUTH_PASSWORD=mypassword
export LIVEDATA_BASIC_AUTH_COOKIE_SECRET=some-random-secret
python -m ess.livedata.dashboard.reduction

Or via CLI (not recommended for production):

python -m ess.livedata.dashboard.reduction \
  --basic-auth-password=mypassword \
  --basic-auth-cookie-secret=some-random-secret

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