Expose discovered MCP tools through the act allowlist (#251)

Second half of the MCP client: the tools the manager discovers become rows in
the existing act allowlist instead of a parallel capability system.

An MCP tool is encoded in the columns that already exist — cmd
["mcp",<server>,<tool>], scope mcp:<server> — so no migration, and
ProposeTool/EnableTool/DisableTool, tool.Matcher and the confirm turn need no
changes. One branch in Executor.Exec routes such a row to the manager instead
of exec, and "mcp" is never run as a binary.

Discovery only ever PROPOSES. destructive comes from the inverse of the MCP
readOnlyHint, so a tool that does not promise to be read-only inherits the
confirm turn, and enabling stays on /tools behind step-up.

Voice args are positional and MCP args are named, so CallPositional binds only
what it can defend: no required properties runs bare, and a read-only tool with
exactly one required string or number gets the tail. Everything else refuses
with ErrNeedsArgs rather than guessing. The read-only condition was learned
against the live Vikunja server: update_task requires only task_id and takes
the rest as optional, so one guessed argument blanked the fields it did not
mention. A partially-filled write destroys what it omits, so a mutating tool
never receives a guessed argument.

Also: a read-only mcp_servers IPC method and an "MCP servers" card on /tools
showing transport, target and state, with the trust level of a local target
spelled out. There is deliberately no call-a-tool IPC method and no run button,
so mutation keeps exactly one path.

Vikunja #251

internal/ipc/server.go

@@ -211,6 +211,10 @@ func (a *storeAPI) MorningStatus(ctx context.Context) ([]MorningRoutineStatus, e
 	return nil, errors.New("store: morning status not available via direct store API")
 }
 
+func (a *storeAPI) MCPServers(ctx context.Context) ([]MCPServerStatus, error) {
+	return nil, nil // no manager behind a bare store: nothing configured
+}
+
 func (a *storeAPI) DayPlan(ctx context.Context) (DayPlan, error) {
 	return DayPlan{}, errors.New("store: day plan not available via direct store API")
 }
@@ -832,6 +836,16 @@ var methodTable = map[Method]handlerFunc{
 	MethodMorningStatus: withoutParams(func(ctx context.Context, api CoreAPI) ([]MorningRoutineStatus, error) {
 		return api.MorningStatus(ctx)
 	}),
+	MethodMCPServers: withoutParams(func(ctx context.Context, api CoreAPI) ([]MCPServerStatus, error) {
+		out, err := api.MCPServers(ctx)
+		if err != nil {
+			return nil, err
+		}
+		if out == nil {
+			out = []MCPServerStatus{}
+		}
+		return out, nil
+	}),
 }
 
 // dispatch unmarshals params for req.Method and calls the matching CoreAPI