Add distributor notification config validation

docs/config.md

@@ -76,6 +76,35 @@ become the environment variable value and overwrite any existing value. One
 trailing LF or CRLF is stripped. Subdirectories, symlinks, invalid filenames,
 missing directories, and unreadable files fail config loading.
 
+### `notify`
+
+`notify.distributor` is validated configuration for distributor notification.
+It is disabled by default. This configuration does not add CLI flags.
+
+- `enabled`: whether distributor notification config is active. Default:
+  `false`.
+- `endpoint`: absolute distributor endpoint URL. Required when enabled.
+  Default: `https://distributor.example.com`.
+- `token_env`: environment variable name that will contain the distributor
+  upload token. Required when enabled. Default: `DISTRIBUTOR_UPLOAD_TOKEN`.
+- `timeout`: distributor operation timeout. Must be greater than zero when
+  enabled. Default: `30s`.
+- `failure_policy`: must be `error` when enabled. Default: `error`.
+- `bundle_id_template`: template for distributor bundle IDs. Default:
+  `weatherreporter.{location_id}.{report_id}.{run_id}`.
+- `idempotency_key_template`: template for distributor idempotency keys.
+  Default: `{bundle_id}`.
+- `report_path_template`: template for the Markdown report path inside the
+  distributor bundle. Default: `{batch_output_name}`.
+
+Supported template variables are `location_id`, `report_id`, `run_id`,
+`artifact_group`, and `batch_output_name`. `idempotency_key_template` may also
+use `bundle_id`.
+
+Rendered report paths must be relative paths with `/` separators. They must not
+contain backslashes, empty path segments, `.`, `..`, `manifest.json`, or
+`.distributor.json`.
+
 ### `missing_source`
 
 - `default`: missing-source behavior for optional sources. One of `error`, `warn`, or `none`. Default: `warn`.