Add env vars to docker addons

[tiborrr]

Add support for addon-specific environment variables

Closes #2896

Summary

Add server-level configuration to inject custom environment variables into addons. Configs are keyed by addon name and support direct values or reading from the process environment.

Configuration

docspell.joex.addons {
  configs = [
    {
      name = "my-postgres-addon"
      enabled = true
      envs = [
        { name = "POSTGRES_HOST", value = "localhost" }
        { name = "POSTGRES_PASSWORD", value-from = { env = "DS_POSTGRES_PASSWORD", optional = true } }
      ]
    }
  ]
}

• value: literal string
• value-from: read from process env. env = source variable name; optional (default: true) — when source unset: true = skip, false = inject empty string

Environment variable override

DOCSPELL_JOEX_ADDONS_CONFIGS_0_NAME="my-postgres-addon"
DOCSPELL_JOEX_ADDONS_CONFIGS_0_ENVS_0_NAME="POSTGRES_HOST"
DOCSPELL_JOEX_ADDONS_CONFIGS_0_ENVS_0_VALUE="localhost"

Running example

Use docspell-addon-example — it logs all DOCSPELL_TEST_* env vars to stderr.

Used config:

# Development config - picked up by sbt when present
# Binds to 0.0.0.0 so the app is reachable from Windows when running in WSL2

docspell.server {
  bind {
    address = "0.0.0.0"
    port = 7880
  }
  backend {
    addons {
      enabled = true
      allow-impure = true
      allowed-urls = "*"
      denied-urls = ""
    }
  }
}

docspell.joex {
  bind {
    address = "0.0.0.0"
    port = 7878
  }
  addons {
    # Example: inject env vars for docspell-addon-example (prints DOCSPELL_TEST_* to stderr)
    configs = [
      {
        name = "docspell-addon-example"
        enabled = true
        envs = [
          { name = "DOCSPELL_TEST_FOO", value = "bar" }
          # value-from: read from process env (e.g. export DS_TEST_BAZ=secret before starting joex)
          { name = "DOCSPELL_TEST_BAZ", value-from = { env = "DS_TEST_BAZ", optional = true } }
        ]
      }
    ]
  }
}