Reconcile config/env docs with actual JSON stdin and launcher variable behavior

[Copilot]

Nightly docs reconciliation flagged contradictory and misleading documentation around payloadPathPrefix, launcher env vars, and DOCKER_API_VERSION. This PR aligns docs with current implementation to prevent misconfiguration in run.sh, run_containerized.sh, and JSON-stdin setups.

• Configuration docs: remove payloadPathPrefix contradiction

  • Removed payloadPathPrefix from the TOML-only / CLI-only table in docs/CONFIGURATION.md.
  • Kept it documented in gateway fields and clarified JSON stdin key naming.

• Environment variable docs: scope by launcher script

  • Updated docs/ENVIRONMENT_VARIABLES.md to split bind/routing variables by script:
    • run.sh: HOST, MODE
    • run_containerized.sh: MCP_GATEWAY_HOST, MCP_GATEWAY_MODE
  • This replaces the previous mixed-scope wording that implied shared usage.

• Docker API version semantics

  • Revised DOCKER_API_VERSION description to clarify it is not read directly by awmg and applies to inherited docker CLI subprocess behavior in helper scripts.

### `run.sh` (non-containerized)
| Variable | Description | Default |
|----------|-------------|---------|
| `HOST`   | Bind address for the gateway in `run.sh`. | `0.0.0.0` |
| `MODE`   | Routing mode flag passed to `awmg` by `run.sh`. | `--routed` |

### `run_containerized.sh` (containerized)
| Variable | Description | Default |
|----------|-------------|---------|
| `MCP_GATEWAY_HOST` | Bind address for the gateway in `run_containerized.sh`. | `0.0.0.0` |
| `MCP_GATEWAY_MODE` | Routing mode flag passed to `awmg` by `run_containerized.sh`. | `--routed` |

[Copilot]

Pull request overview

Aligns configuration and environment-variable documentation with the gateway’s actual JSON-stdin and launcher-script behaviors to prevent misconfiguration when running via run.sh, run_containerized.sh, or piping JSON config.

Changes:

• Split bind/routing environment variables by launcher script (run.sh vs run_containerized.sh) in docs/ENVIRONMENT_VARIABLES.md.
• Clarified DOCKER_API_VERSION affects only inherited docker CLI subprocess behavior (not read by awmg directly).
• Updated docs/CONFIGURATION.md to keep payloadPathPrefix documented under gateway fields and removed it from the “TOML-only / CLI-only” table.

Show a summary per file

File	Description
docs/ENVIRONMENT_VARIABLES.md	Separates script-scoped variables and clarifies Docker API version semantics for helper scripts.
docs/CONFIGURATION.md	Adjusts payloadPathPrefix documentation and removes it from the “TOML-only / CLI-only” options table.

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• Files reviewed: 2/2 changed files
• Comments generated: 1