fix: infra: CI broken on main — missing WOODPECKER_PLUGINS_PRIVILEGED server env + misplaced .woodpecker/ops-filer.yml in project repo (#779)

Part 1: Add WOODPECKER_PLUGINS_PRIVILEGED to woodpecker service environment
in lib/generators.sh, defaulting to plugins/docker, overridable via .env.
Document the new key in .env.example.

Part 2: Delete .woodpecker/ops-filer.yml from project repo — it belongs in
the ops repo and references secrets that don't exist here. Full ops-side
filer setup deferred until sprint PRs need it.

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

lib/generators.sh

@@ -295,6 +295,7 @@ services:
       WOODPECKER_AGENT_SECRET: ${WOODPECKER_AGENT_SECRET:-}
       WOODPECKER_DATABASE_DRIVER: sqlite3
       WOODPECKER_DATABASE_DATASOURCE: /var/lib/woodpecker/woodpecker.sqlite
+      WOODPECKER_PLUGINS_PRIVILEGED: ${WOODPECKER_PLUGINS_PRIVILEGED:-plugins/docker}
       WOODPECKER_ENVIRONMENT: "FORGE_TOKEN:${FORGE_TOKEN}"
     depends_on:
       forgejo: