docs(rfd): Update RFD 081 with ToggleScope, string allow_toggle values

[JeanMertz]

Replace DirectiveScope with ToggleScope throughout the design, and switch allow_toggle from a bool to a string enum: "any" (formerly true / Always) and "never" (formerly false / Never). The "any" spelling is deliberate — it cannot be confused with the legacy enable = "always" shorthand, which means the opposite (locked-on).

Clarify that Serialize operates on stored optional fields rather than effective_enable(), and that the bool shorthand is only emitted when both fields are set and allow_toggle is Always. A { state: Some(true), allow_toggle: None } therefore serializes as { state = true }, never true.

Expand the apply_tool_use validation note to explain this is a config-eligibility check, not a delivery guarantee, and that runtime mismatches (tool absent from the resolved list after MCP startup) are left to the runtime access-control track.

Move the assistant.tool_choice locked-off validation from config-resolution time to AppConfig::validate, which is the only validator that sees both assistant and conversation.tools.

Add a Phase 1 task to make deep_merge_toml recurse into inline tables (as_table_like_mut / as_table_like), fixing the case where jp config set conversation.tools.foo.enable.state ... against an inline enable = { ... } would silently drop allow_toggle.

Update the RFD cross-reference tasks to include RFD 056, 057, and 083 updates in Phase 4, and clarify that existing bool/string payloads written to conversation.tools.*.enable remain valid under the new deserializer.