docs(074): correct per-server tool_discovery_interval row

The server-fields table still described per-server tool_discovery_interval
as forward-compatible only, claiming the periodic sweep runs on the global
cadence. The runtime now honors per-server overrides
(ResolveToolDiscoveryInterval, internal/config/config.go:92), so the row now
states the per-server value overrides the global/default cadence and 0s
disables the sweep for that server only, matching FR-013/SC-006 and the
prose at docs/configuration.md:148.

Related #608

Author: Dumbris

docs/configuration.md

@@ -207,7 +207,7 @@ the proxy.
 | `env` | object | No | Environment variables for stdio servers, or for the locally-launched child of an HTTP/SSE server |
 | `launcher_wait_timeout` | duration | No | When `command` is set together with an HTTP/SSE `url`, how long mcpproxy waits for that URL to become reachable after spawning the child (e.g. `"15s"`, default `"30s"`) |
 | `health_check_interval` | duration | No | Per-server override for the global [`health_check_interval`](#discovery--health-checks). `"0s"` disables the liveness probe for this server only. Range: `5s`–`1h`. Omit to inherit the global value. |
-| `tool_discovery_interval` | duration | No | Per-server override for the global [`tool_discovery_interval`](#discovery--health-checks). Accepted and persisted for forward-compatibility; the periodic index rebuild currently runs on the global cadence. Range: `30s`–`24h`. Omit to inherit the global value. |
+| `tool_discovery_interval` | duration | No | Per-server override for the global [`tool_discovery_interval`](#discovery--health-checks). Overrides the global/default cadence for this server only; `"0s"` disables the periodic tool-discovery sweep for this server (connect-time and reactive `list_changed` discovery still run). Range: `30s`–`24h`. Omit to inherit the global value. |
 | `oauth` | object | No | OAuth configuration (see [OAuth Configuration](#oauth-configuration)) |
 | `isolation` | object | No | Per-server Docker isolation settings (see [Docker Isolation](#docker-isolation)) |
 | `enabled` | boolean | No | Enable/disable server (default: `true`) |