TODO: migrate mcp.servers editor to the per-field surface

Context

web/src/components/sections/FieldForm.tsx renders mcp.servers through ObjectArrayEditor — a JSON-array editor that round-trips the whole Vec<McpServerConfig> through set_prop("mcp.servers", "<json-array>"). The editor was a bridge built before the runtime supported per-element property addressing on Vec<T> + #[nested] list sections (see commits adding route_vec_path, the macro's #[natural_key] arm, and Section::McpServers).

That bridge is no longer necessary for mcp.servers. The runtime now exposes the same per-element surface that HashMap<String, T> sections have always had:

• GET /api/config?prefix=mcp.servers.<name> returns per-field entries for that server.
• PUT /api/config/<path> with path = mcp.servers.<name>.<field> edits a single field.
• POST /api/config/map-key?path=mcp.servers&key=<name> creates a new entry (already used by the existing editor for the whole-array path).
• DELETE /api/config/map-key?path=mcp.servers&key=<name> removes by natural key.
• POST /api/config/map-key/rename?path=mcp.servers&key=<old>&new_key=<new> renames the natural key in place, with validation.

The zerocode TUI uses exactly this surface today (it dispatches mcp.servers through the same OneTierAliasMap rendering as risk_profiles, cron, etc.). The dashboard should do the same.

Migration sketch

1. In web/src/components/sections/FieldForm.tsx, detect that mcp.servers (or any ListSection whose value type now opts into #[natural_key]) should be rendered through the existing per-alias path, not ObjectArrayEditor. The runtime reports the section's shape in /api/config/sections (shape: "one_tier_alias_map"); the dashboard already special-cases that shape for the other sections.
2. Surface the new error strings as toast/banner messages:
   • "natural key … is ambiguous in mcp.servers: N entries share it; fix duplicates first" — the runtime emits this for get_prop / set_prop / rename_map_key against a duplicated name.
   • "mcp.servers.name is the natural key for mcp.servers entries and is read-only; use config_map_key_rename to change it" — surfaces if any code path still tries to PUT to mcp.servers.<name>.name directly.
3. Drop the ObjectArrayEditor code path for mcp.servers only (other Vec<T> schema fields — peripheral.boards, classification, etc. — have not opted into #[natural_key] yet and still need the JSON-array editor).

Wider follow-up

Each of the other Vec<T> + #[nested] schema fields can opt into the same per-field surface by adding #[natural_key = "<field>"] at the field declaration site:

• Vec<ClassificationRule> — natural key is hint.
• Vec<EmbeddingRouteConfig> — natural key is name.
• Vec<GoogleWorkspaceAllowedOperation> — natural key is name.
• Vec<ModelRouteConfig> — natural key is name.
• Vec<NevisRoleMappingConfig> — natural key is name.
• Vec<PeripheralBoardConfig> — natural key is name.
• Vec<ToolFilterGroup> — natural key is name.

Adding the attribute is one line per type; the dashboard then needs the same shape-aware dispatch from step 1 above. Coordinate the schema opt-ins with whoever maintains the dashboard so the JSON-array fallback isn't deleted before the per-field path is wired up for those sections.